IMHO all this falls into category "optimization". It's nice to think about it but first the real problem has to be solved. My impression - from a perspective of guy who knows nothing about the details - the additional null painter step looks reasonable.
For sure it is an optimisation, but it might be justified since it is a severe regression compared to 1.3.
Also, notice the null painter step in itself will not solve the crashes. Introducing it to avoid excessive repaints due to nested update calls is only a band-aid.
A better fix is to go to the root of the cause, and in this case, as mentioned in another post, I believe the right fix is to either omit or postpone the qApps->processEvent calls during update.
Of course, excessive update calls from other places, as found by George, should also be nailed. (Notice, that the optimisation as sketched out would reduce the cost of superfluous update calls to a metrics and null-paint job only - the outcome would be identical to before, and no painting on screen would be necessary).
Regards, Asger
