I always check pressure at 6 o'clock and have not had that problem but obviously, it's possible. I check pressure every ride day.
Since Tom's buddy had it 3 times there might be something else at play.
Old beads get sticky, I only re-use them twice now(3 times total).
Mounting a new tire with more than a minimum of tire lube could be a factor.
In any case, if you put a puff of air in before checking pressure you can blow any beads off the valve.