Hi John, thanks for the info.

I may have an alternative explanation. The last 2 weeks in which I had overexposed shots, the room temperature was around 35 deg C in the room I use for developing. And it may be that developing temperature may have been a few degrees higher than normal...which may have caused the problems. I will have another look at the "problem negatives" to look whether the problem is overexposure or overdevelopment. During these two "hot weeks", I developed 3 rolls of the om-2n and just one of the canonet and none of my other cameras...

Anyway, I'm now in China for work for a a few days. I've shot quite a few rolls here. I will develop them when I get back home and hopefully see whether they are OK or not...