if you draw out the CL/alpha curve, you'll see that over the stallnig angle, say 14deg. increase in AoA results in a reduction of lift. Therfore in the stall, you are CL/Alpha Unstable.
Wing drops (due to minor differences ect)
AoA increased - over stall angle so lift further reduces.
Wing drops more.
I think the dragy barn door type flaps on some trainners exentuate the loss of lift and drag, also at a slower speed, a reduction is a bigger percentage of total airspeed giving the drop more gusto.