Compiler errors in unreferenced scripts

I want to experiment with some modifications on the standard Joystick.js script, so I made a copy of it. However, now my build fails because the global helper class Boundary is defined twice, even though nothing in my scenes is actually referencing one of the definitions. I can fix this easily enough by renaming the class, but I don't understand why a compile script error in an unreferenced script should prevent a successful build. Thanks!