Stub model imports broken inside a Solution

I wasn't quite sure if I should post it here or on the bug tracker. As already reported as an issue the stub model import seems to be broken. For me is is broken even in MPS 3.0 not since 3.2 as stated in the report.

In my understanding that means that I can't use external java libraries at all or am I missing something? Is there a workaround? That seems like a issue that I thought many people would have, but the priority is only set to normal.

Thanks in advance.