After doing what Brian suggested, you might also try the following:
1) replace the batteries in the HR12A again. There is a remote possibility that you have a bad battery. You might want to try cleaning the battery contacts, as well.
2) Rotate the HouseCode wheel all the way around - sometimes the contacts on it get dirty. (This probably won't do anything, since you reported that it WAS transmitting on the correct housecode, just the wrong unit code - but it doesn't hurt to try).
3) verify that the HouseCode/Unit codes are correct on your lights. Verify that you can control them manually from within AHP.
4) Try the HR12A again, but use it right next to the CM15A. Unmodified, the CM15A had a very limited RF range. It could be that you are just at the edge of that range, so the commands are getting garbled coming through.
Do you have any macros, that might be turning on A1? (perhaps on a different housecode, and unit 3?)
Try rotating the Housecode wheel to a different housecode, and check the Activity Monitor to see if the HR12A transmits anything on the other housecodes.