I've always had the same problem with lamp, and sometimes appliance, modules from X10 regardless of age following some power outages. ACT, SmartLabs (Insteon), Marmitek, etc. never misbehave. It's enough of an annoyance that I designed a workaround for it into the HA logic platform I'm writing. Status of X10 modules is tracked as "Received State" and "Desired State". They usually are kept in sync, but if the UPS detects that the utility power is out, only "Desired State" is updated (since no X10 modules would be online to receive signals). Once the utility power is restored, an algorithm compares "Received State" to "Desired State". Based on the device models in the database, it knows which modules remember their state and need to be sent commands to meet the "Desired State" or left alone, and which modules need to be sent whatever the current state should be regardless because their state is unpredictable.
I'm not aware of an "official" fix for this issue.
But bottom line is that I don't expect that the WM100 sent any commands to turn your lights on; I think it's an issue of your lamp/fixture modules not remembering their state correctly after a power outage. Reviewing this, I'm noting that I put a lot of work toward solving something that very rarely affects me. That's probably a good indicator of why no one else has bothered to solve it and why my platform may never be finished.