Regards the Williamtown one in 1988 with PC and passenger, this may not be fully correct or perhaps just rumour control, but my understanding was that the PFL pattern being flown was a circular one (unlike the rectangular pattern used by CT4s at 1FTS, for example) during which a frequency change to tower was required. The implication was that having to look in for the freq. change while in the turning glide led to loss of airspeed and a stall with wing drop - unsure if there was partial flap down at the time, and not having flown the Winjeel I can't vouch for it but again was of the understanding that they could drop a wing fairly well during the stall.
As noted, this is just what I remember of being told or possibly of reading some version of the accident report - apologies for inaccuracies.