I've just spent a nice chunk of time looking over this too, and the only interesting result I got was after useing only M1 and M3 the error: NOT IMPLEMENTED YET. at test1.perl line 60 BEGIN failed--compilation aborted at test1.perl line 60. (The line is use M3 ..., in case our line numbers are off.) It appears to be upset at foo, and aborting compilation. What we really need is to step through the BEGIN blocks with the debugger, but I don't even think that's possible. Hopefully that's a helpful clue, John; it's the best I can do.