Loop... Hole, My quote............
If, on approach, I see an aircraft at the holding point with strobe lights ON, I have only one reaction - Go Around!
Your quote..........
I have therefore been at the hold with white flashing and no-one's gone around on me yet. Is it only a matter of time?
Yes, I think that it's only a matter of time. It's pretty much universal in the 2 airlines that I've worked for.
If I get a clearance "After the landing XX line up and wait behind", it's hands OFF the Strobes, Landing Lights etc. until the landing aircraft has passed our position at the hold. Then it's turn everything ON, get on the runway, and wait your Takeoff clearance.
Regards,
Old Smokey