Ok.
replacing "do" or "eval `cat file.pl`" with "require" things got a lot better.
but, for future reference: i think(!) the main problem is/was Tk's waitVariable. if i create the widget in one file, and watch a waitvariable with code from another file, i get to wait forever, it seems. the "waiter"-code simply doesnt get it.
i'll try to create a simple test-case, and ask the Tk-guys about that....