All classes generated from Scala sources, have a classfile attribute that tells the name of the source they originate from. Except for those compiled from Java (we have a couple, such as `BoxesRunTime`). The end-result is that you can't really debug or set breakpoints in these files.
By default, `javac` sets this attribute for all classfiles it generates.
I guess this is unintentional, but it is pretty annoying in the debugger.