The WS467 wall switch (and I suspect it's variations, as well) does indeed "randomly" turn on.
This info will void the x10 warranty, however this fix works.
Specifically, under the correct conditions, a WS467 can "glitch" on due to a power spike from a large bank of magnetic ballast fluorescents on the same circuit, large motor, etc. And filter caps across the 78566 chip, resistor change in the "button" line nor MOVs do not help.
The solution is actually quite simple, once it is figured out. The 78566 chip in the WS467 contains 2 unused pins (pin #8 and pin #9) who's function is unknown to me. However, manipulation of pin #9 can cause the WS467 to turn on the light.
After discovering this, I have since tied pin #9 to -v and the "random" light turnons have stopped. My personal preference is to install a 10K 1/8-1/4w resistor across the top of the ic between pin #9 and pin #18. A hard wire will probably be ok, but not acceptable standard practice when dealing with bidirectional I/O pins.
Hope this helps, Marksrobotics