I've been using a combination of Bezier Masking (BM) and Pan/Crop to, for instance, create a screen divided into three sections, with different events running in each. I've noticed that, at times, adjusting the Pan/Crop will adjust values within the BM parameters - particularly the Location coordinates. On one occasion the whole combination appeared to 'stick' - couldn't seem to get a full length column no matter what I tried - and my only way out was to delete BM from the effects chain, re-add it and start again.
The problem is intermittent (i.e. I haven't yet tracked it down to a particular action within BN or Pan/Crop) and is, so far, fixable so I'm not inclined to gather detailed diagnostics - at this stage I'd just be interested to hear if anyone else is experiencing similar.