I have just been through the very same issue.
The problem is due to a split package (org.hamcrest) between o.h.core and o.h.library but Mockito does not specify this in the import., so if you use both of the Hamcrest bundles in your application - and you often do - then you're in for trouble...
I ended up resolving this with a special bundle that combines the two packages and re-exports all the packages. The MANIFEST.MF is listed below. Note that there are absolutely no code in the bundle, so it just consists of the manifest.
Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: AGETOR 5: Combination of Hamcrest Core and Hamcrest Library
Bundle-SymbolicName: com.agetor.core.hamcrest.combined
Bundle-Version: 1.3.0.qualifier
Bundle-Vendor: Bording Data A/S
Bundle-RequiredExecutionEnvironment: JavaSE-1.7
Export-Package: org.hamcrest;version="1.3.0",
org.hamcrest.beans;version="1.3.0",
org.hamcrest.collection;version="1.3.0",
org.hamcrest.core;version="1.3.0",
org.hamcrest.integration;version="1.3.0",
org.hamcrest.internal;version="1.3.0",
org.hamcrest.number;version="1.3.0",
org.hamcrest.object;version="1.3.0",
org.hamcrest.text;version="1.3.0",
org.hamcrest.xml;version="1.3.0"
Require-Bundle: org.hamcrest.core;bundle-version="1.3.0",
org.hamcrest.library;bundle-version="1.3.0"
This really is a terrible hack, but the Hamcrest team seems to think the use of non-sealed packages in Java is a good thing and is there to be used ;-) Unfortunately, these does not play well in the OSGi environment. (I believe I found the above solution on bugzilla, though I lost the reference).