I saw on the console a ClassCastException, when I triggered the code completion very fast: 
java.lang.ClassCastException: org.eclipse.jdt.internal.codeassist.impl.AssistSourceMethod cannot be cast to org.eclipse.jdt.core.IType
	at org.eclipse.recommenders.internal.completion.rcp.proposals.ProcessableProposalFactory.newMethodDeclarationCompletionProposal(ProcessableProposalFactory.java:181)
	at org.eclipse.recommenders.internal.completion.rcp.proposals.ProcessableProposalFactory.create(ProcessableProposalFactory.java:82)
	at org.eclipse.recommenders.internal.completion.rcp.ProcessableCompletionProposalComputer.computeCompletionProposals(ProcessableCompletionProposalComputer.java:96)
	at org.eclipse.recommenders.internal.completion.rcp.RecommendersAllCompletionProposalProcessor.computeCompletionProposals(RecommendersAllCompletionProposalProcessor.java:63)
	at org.eclipse.jdt.internal.ui.text.java.CompletionProposalComputerDescriptor.computeCompletionProposals(CompletionProposalComputerDescriptor.java:333)
	at org.eclipse.jdt.internal.ui.text.java.CompletionProposalCategory.computeCompletionProposals(CompletionProposalCategory.java:337)
	at org.eclipse.jdt.internal.ui.text.java.ContentAssistProcessor.collectProposals(ContentAssistProcessor.java:325)
	at org.eclipse.jdt.internal.ui.text.java.ContentAssistProcessor.computeCompletionProposals(ContentAssistProcessor.java:282)
	at org.eclipse.jface.text.contentassist.ContentAssistant.computeCompletionProposals(ContentAssistant.java:1839)
	at org.eclipse.jface.text.contentassist.CompletionProposalPopup.computeProposals(CompletionProposalPopup.java:566)
	at org.eclipse.jface.text.contentassist.CompletionProposalPopup.access$16(CompletionProposalPopup.java:563)
	at org.eclipse.jface.text.contentassist.CompletionProposalPopup$2.run(CompletionProposalPopup.java:498)
	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
	at org.eclipse.jface.text.contentassist.CompletionProposalPopup.showProposals(CompletionProposalPopup.java:492)
	at org.eclipse.jface.text.contentassist.ContentAssistant.showPossibleCompletions(ContentAssistant.java:1665)
	at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor$AdaptedSourceViewer.doOperation(CompilationUnitEditor.java:183)
	at org.eclipse.ui.texteditor.ContentAssistAction$1.run(ContentAssistAction.java:82)
	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
	at org.eclipse.ui.texteditor.ContentAssistAction.run(ContentAssistAction.java:80)
	at org.eclipse.jface.action.Action.runWithEvent(Action.java:499)
	at org.eclipse.jface.commands.ActionHandler.execute(ActionHandler.java:119)
	at org.eclipse.ui.internal.handlers.E4HandlerProxy.execute(E4HandlerProxy.java:90)
	at sun.reflect.GeneratedMethodAccessor24.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:56)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:243)
	at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:224)
	at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
	at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:167)
	at org.eclipse.core.commands.Command.executeWithChecks(Command.java:499)
	at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:508)
	at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:213)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.executeCommand(KeyBindingDispatcher.java:285)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.press(KeyBindingDispatcher.java:504)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.processKeyEvent(KeyBindingDispatcher.java:555)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.filterKeySequenceBindings(KeyBindingDispatcher.java:376)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher.access$0(KeyBindingDispatcher.java:322)
	at org.eclipse.e4.ui.bindings.keys.KeyBindingDispatcher$KeyDownFilter.handleEvent(KeyBindingDispatcher.java:84)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1080)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4165)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1466)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1489)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1474)
	at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1503)
	at org.eclipse.swt.widgets.Widget.sendKeyEvent(Widget.java:1499)
	at org.eclipse.swt.widgets.Canvas.sendKeyEvent(Canvas.java:496)
	at org.eclipse.swt.widgets.Control.doCommandBySelector(Control.java:1060)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5648)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSend(Native Method)
	at org.eclipse.swt.internal.cocoa.NSResponder.interpretKeyEvents(NSResponder.java:68)
	at org.eclipse.swt.widgets.Composite.keyDown(Composite.java:594)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5558)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
	at org.eclipse.swt.widgets.Widget.callSuper(Widget.java:221)
	at org.eclipse.swt.widgets.Widget.windowSendEvent(Widget.java:2104)
	at org.eclipse.swt.widgets.Shell.windowSendEvent(Shell.java:2318)
	at org.eclipse.swt.widgets.Display.windowProc(Display.java:5620)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSendSuper(Native Method)
	at org.eclipse.swt.widgets.Display.applicationSendEvent(Display.java:5057)
	at org.eclipse.swt.widgets.Display.applicationProc(Display.java:5206)
	at org.eclipse.swt.internal.cocoa.OS.objc_msgSend(Native Method)
	at org.eclipse.swt.internal.cocoa.NSApplication.sendEvent(NSApplication.java:128)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3648)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1113)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:997)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:138)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:610)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:567)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:354)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:181)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:636)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:591)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1450)
	at org.eclipse.equinox.launcher.Main.main(Main.java:1426)