I have a class named "Änderungsprotokoll" (changelog). First character is 0xC4 in Unicode, a German umlaut. This class gets compiled always, and along with it all files depending on it, even if I did not make a single change to any file. Since I have some central classes named that way, this basically prevents imcremental build.
Now that I know about this, it is not so much trouble renaming the classes, thanks to Shift-F6 , but coming up with the right guess what prevented incremental build took me about half a year and probably cost days in compile time. So if you deam it not worth fixing, add it to the known issues.