x10 switch problem?

["Amadeus W.M." <amadeus84@xxxxxxxxxxx>]

I have a wall motion sensor switch that I've been using happily for some
2 years now. It controls the ceiling fixture which up until today was a
ceiling fan that came with the house.

Today I took the fan off and I installed a new fixture. It uses a 30W
fluorescent ring bulb. The light is off when the switch is off, it's on
(and steady) when the switch is on, but it flickers continuously when the
switch is in the middle (i.e. set to motion detection). Is this normal?
Must I have an incandescent bulb with that switch?

I installed the switch and the light fixture, so I may have done
something wrong, but so far nothing has blown up yet.