When I turn "off" my bathroom vent fan, my shower light turns on momentarily until the fan stops spinning.
Both the light and the fan are wired in parallel on the same circuit.
If I drop the shower light (Utilitech 65-Watt Dimmable LED Recessed Retrofit Downlight) suspended in the air (i.e. the three prongs no longer touch the can), the problem goes away. If I push it back in the can, the problem returns.
At this point I've ruled out everything but paranormal activity.