How to access plugin's manifest ?

Using J2SE one can do the following getClass().getPackage().getImplementationVersion() and obtain the "Implementation-Version" value from the Manifest.mf of the jar that defined the class.

I've tried using that in a plugin, I obtain a Package instance, but it doesn't seem to be correctly bound to the jar where the class comes from : it's manifest attributes are null.

Is there any reason , maybe dealing with the pico container ? or is this a bug ?