May have something to do with the starting on the ballast. Rapid start
or instant start. A ballast in a fixture is essentially a transformer.
A transformer with an inductive load.

Reference.


http://www.safeelectricity.org/results.asp?ID=213

What is nuisance tripping of a GFCI?
It takes only 5 mA (0.005 A) of current leakage from the hot wire to
the ground to cause a GFCI to trip. A small amount of leakage current
may be difficult to avoid in some normal circuits. Hand-held power
tools do not cause a tripping problem if the tool is maintained in
good condition. Some stationary motors, such as a bathroom vent fan or
fluorescent lighting fixtures, may produce enough leakage to cause
nuisance tripping. Another problem may be a long circuit with many
splices. If possible, keep GFCI circuits less than 100 feet long. To
avoid nuisance tripping, a GFCI should not supply:

Circuits longer than 100 feet
Fluorescent or other types of electric-discharge lighting fixtures
Permanently installed electric motors



On Mon, 16 Oct 2006 03:11:21 GMT, "Toller" wrote:

I have a fluorescent light plugged into and outlet that comes BEFORE a GFCI
outlet on a circuit.
About 5% of the time I turn the light off (I have a switch leg going to that
outlet) the GFCI trips.
It only happens when I have an air filter turned on that is plugged into the
GFCI.

It is not clear to me why turning off the light would affect the GFCI coming
after it. (Yes, I do have the GFCI installed correctly; not backwards.)
Even if there was a ground fault, and I can't see why there should be one,
the GFCI wouldn't see it.

Any ideas?