Riiight... One day we saw you join the server and decided, "Hey, you know what would be fun? lets never let anything spawn for Grimper!"...
Ya, no. One more time: There is nothing wrong with the code, take your complaints elsewhere since it will not be magically fixed due to your constant whining. Either:
1) Move to where the mobs are.
2) Wait for 1.0 to change things up a bit and hope it does something.
3) Open up the code and design a patch for the notchcode to 'fix' it.
4) leave it alone and stop complaining.
EDIT: I personaly suggest 2, it seems the most likely to happen if any will.