NCPatrolAR, I have a TLR-1S on one of my G19's, I've been
shooting it that way (200-250 rnds per week) for the last
6 months and have not encountered this problem either. The
only thing I would conclude is that with the light activated in
momentary position while shooting, the recoil is causing the
operators thumb to come off or lighten pressure enough to
get the required double-tap for strobe mode.