Everything works fine in Eclipse 3.5.x/3.6.x/3.7.x/3.8.
However when I tested on Eclipse 4.2 the buttons appeared on the toolbar with a label on the right.
At first I thought it was some parameter too many in the plugin.xml section command inside toolbar.
I tried to get rid, first of the label attribute and then also of the tooltip one.
However it seems that the problem is that the shown label is the attribute "name" of the contributed wizard ( extension point="org.eclipse.ui.newWizards").