Mostly I have had great results with mixed code - however, occasionally I will mess with some java code, and then an unrelated java class will stop compiling - as it is unable to find the scala class it depends on (not talking circular deps or anything fancy). Note that it won't show up with syntax errors (even the content assistance works correctly) but it just wont "make" when I try to build it, or run tests.
I use maven to build as well, and it is able to build correctly (even a clean build).
To correct - I usually comment out the offending bits, make, and then restore it and all is well.
Anyone else seen this?