Incremental compilation causes "mvn clean compile compile" to fail

With <useIncrementalCompilation>true</useIncrementalCompilation>, my build fails if I do "mvn clean compile compile". From the comment in MCOMPILER-205, I understand that incremental compilation deletes the "classes" directory. But it seems that it doesn't delete the "generated-sources" directory.

When I do "mvn clean compile" and "mvn compile", the second build fails. However, if I delete the "generated-sources" directory between the 2 builds, they both succeed.

So I guess the bug here is that incremental compilation doesn't delete the "generated-sources" directory.