Hi Mario,
I am not familiar with Eclipse plugin development so I don't know how I can make it easier to reproduce on your side. I just tested with the default drools sample project and change a "when" to "when1" in Sample.drl.
However, I am almost sure this is caused by the latest commit. I did a git revert to the previous commit (5b7101f13cf6eb6bb3cea37638b0d9d982a6b10b "disabled enforce-plugin-version rule"), and this error can be detected (see attached ScreenShot1.png). However, the plugin built with the latest commit can't detect it (ScreenShot2.png). I tried to clean/rebuild the project and re-import, but the result is all the same.
Please let me know if I can provide more information by any means.
Thank you very much.
Jinghai