My coworkers (Mac OS X 10.6, Win 7) and I (Win 7) recently upgraded to IntelliJ 10.5.1 together with the Scala plugin 0.4.1183 and using Scala 188.8.131.52, and we have all seen buggy highlighting in Java source files (good code red in .java files). For me it was very flaky--I reinstalled IntelliJ 10.5.1 together with Scala plugin 0.4.1183 and haven't seen the problem again (though it's hard to reproduce so it may come back). My coworker has says that sometimes toggling the Scala plugin "type aware highlighting" can intermittently make the problem go away, and my other coworker demonstrated that disabling the scala plugin fixed the problem. Have others seen this problem? Can Java source highlighting errors be caused by the Scala plugin? Any ideas for fixing it, maybe reverting to a previous plugin? It looks like my coworkers will have to disable the scala plugin until we identify what's happening here. Thanks for any ideas!