CM15a's antenna sucks. Noisy and in some cases doesn't work at all. Don't send anything from its antenna to the power line.
Noisy environments, half-dead motion sensors, etc. will consistently make the same (bogus) commands show up. All Lights On/All Off seem to be the easiest to slip by.
I use two WGL transceivers, one on the power line for remote control (for a couple of sticky switches) and one that connects to the serial port of a PC and sends the commands directly to Misterhouse (primarily for motion and brightness sensors.) That way the constant chatter from the sensors does not step on manual intervention (pressing a button on a PalmPad, camera remote, etc.) There is a very good article out there about how to pick which house codes to use. There are only six of sixteen that are comfortably spaced (has to do with the raw codes received by the transceivers and how they differentiate them.) Within these house codes, there are six units codes that are similarly spaced. So if you can get by with 36 discrete codes, you will have virtually trouble-free operation. How to get by like that? Scenes. How else? IR control (PalmPads suck!)
Oh and watch out when looking up the "two bits apart" X10 address spacing page (that should Google it) as there are two. One is correct, one is wrong. They both had the same idea, but only one guy got it right. Hopefully the other one has been taken down. Seems like A, D, F, G, H and P are the "safe" ones, but don't quote me on that. Despite using scenes and other tricks, I still can't condense my setup down to 36. Sure enough, it is the few modules that reside on the "unsafe" codes that occasionally turn on/off by themselves. The more motion sensors you have (especially the light colored models), the more "ghosts" you will have.