Pondo,
Try not to be so hard on the X10 programmers. A couple of years ago the company got rid of their programmers (or they left, I forget). Just recently we got some new guys that inherited the code sans documentation.
IMHO, they've done a bang up job piecing it all together, and they're looking for the source of the problem.
They're really trying, but the code is a mile long and had had too many hands on it, and no one told the new guys what was done, or when.
The code you are seeing is a result of a security sensor checking in. This is strictly an encrypted RF receive. The only way that action will make it to the powerline to affect your x10 system is if you had it set to trigger a macro, sending a plc command. Since the source has yet to be tracked, I doubt that you can even map THAT particular sensor to a macro.
If I had to guess, I'd say it's being generated by the CM15A itself. The CM15 has the ability to send an encrypted security command, so that it can emulate a security remote to disarm an X10 alarm system, but I don't think the coding on this has ever been perfected.
For now, it's a glitch that we all live with, but just mentally ignore it. It doesn't hurt anything.
It's kinda like all the radio signals being received where you live. They're all there, but you're not tuned into all of them at any one time, and they're not affecting your radio, or cell phone or garage door opener or wi-fi. Infact, without the proper receiver, you'd never know they were there.