Consider the case where you have two projects:
The first project contains a type descriptor which imports another type descriptor from the second project.
When JCasGen is invoked with the option to limit generation to the first project, then JCas classes for the types imported from the second project are still generated. Why? Because "/my/project" is a prefix of "/my/project1". JCasGen thinks that "/my/project1" is within the scope of "/my/project".
This could be fixed by ensuring that paths terminate in a "/".