If I change the project JDK and make the project (using ctrl-f9 or the automatic recompilation that is triggered by running or debugging), IDEA does not automatically recompile the project. I have to do a manual rebuild. It could be argued whether this is a bug or a feature (not having to rebuild just because the JDK was changed). I guess that my interpretation of "make" is that it should place the project in exactly the same state as a rebuild, while reusing existing results whenever necessary. A manual rebuild should only be necessary if there is a bug in the make system. (I often run and debug my project under JDK 1.6, but sometimes I want to check that it still works under JDK 1.5, or compile a set of class files to be distributed to computers that only run JDK 1.5. If I change the JDK and run a program, I get "bad version number in .class file", since I'm still using the old class files compiled with JDK 1.6.)