Slightly OT question

["BruceR" <razrbruce@xxxxxxxxxxxxxxx>]

I installed a couple of simple Leviton motion detector switches each to
control incandescent bulbs in closets off a bathroom.  They work just
swimmingly except for one problem:  if the exhaust fan over the toilet
is turned on - even briefly - one or both (usually both) of the closet
fixtures will go into a "strobe" mode flashing on and off very quickly.
To resolve the issue the manual switch must be turned off then back to
auto for normal operation.  I am assuming the fan is on the same circuit
but I'm not there now to check that.  Any ideas as to the cause and,
more importantly, a fix?