Knowing how X10 signals are transmitted on the powerline, it would be difficult to mimic the pattern that causes the problem you describe. I have seen the noise from multiple compact fluorescent lights sum together with sufficient energy to morph one X10 command into another. It might be possible for them to create a complete X10 command, but I never saw that in my testing.
I recently read a report of a similar problem. As I recall, water had dripped onto a maxicontroller and caused it to transmit commands by itself. Wireless remotes could do the same. I would look for some X10 device transmitting a signal. It might not even be in your house. A signal meter is the best way to find out what is going on.
Jeff