Can't really think of why it may be doing this, so I'd just try a bunch of stuff, like...

1. Are your other game settings being saved?
2. If you change something else, does it work (like 16-19)?
3. Are there any weird values in the settings (something other than 00 thru 03)?
4. Reset all audit settings one-by-one using the button on the MPU (basically, classic Bally version of a factory reset).
5. Check connectors between sound board and MPU.

things you may not be able to try, but might also help isolate the problem...

Swap MPU with another
Swap sound board with another
Swap 5101 with another
Swap ROMS with others

^^^...If its a possible bad bit on the PIA, you can try swapping the two PIA's and see if the problem moves...

EDIT: Sorry, I read that wrong -- 'PIA on the sound board'. But you could try swapping a PIA between the MPU and sound board.

I can see how that was confusing, but, no, only swap like parts -- I meant swap the 6821 FOUND on the MPU board (this would be either U10 or U11) with 6821 found on the sound board (not sure what U no. that is).

If you're new to poking around with pinball electronics, you want to use extreme caution when swapping chips around. You should probably read up on the beginner posts on pinwiki, pinside, other sources, etc, the chips have to be oriented correctly, pins can bend under the sockets, etc, there are plenty of pitfalls if you don't know what you're doing.