This one I don't know about. In the U.S. it's pretty
common
wisdom that it's worthwhile practicing the egress with
a
chute, instead of always unbuckling the chute and leaving
it
in the aircraft. I don't know if unbuckling under
emergency
stress is a real concern. I think practicing egress
while
wearing the chute *is* a good idea, as it's harder
than you
think.

Our ex-CFI nearly baled out of an open cirrus having
removed his straps AND parachute. Fortunately (or unfortunately
depending on whether you liked him or not) he realised
when he was only half way out and put it back on before
jumping.
The local newspaper report said:
'Club members watched in horror as his parachute opened'