Is there a physics explanation for this? Even the seasoned riders at the
bike shop give me a wierd look when I tell them I hardly ever use the rear
brake.

FWIW, if you lose traction on the front in a turn, it is very likely you
will crash. If you lose traction on the rear in a turn, it is usually
recoverable unless your lean angle is extreme.

Braking the rear in a turn may cause the rear to skip causing the effects
you mentioned. But when you brake with the front, weight is pushed forward
onto the front wheel and giving it heavier steering, etc.

--
Phil, Squid-in-Training