I can confirm that Timothys Hack with downgrading the mentioned packages is a working workaround for the kwin crash issue (no more crashes when resizing the window etc. as well. (Unfortunately it does not tackle the performance issue in QT applications which I hoped was correlated with this problem but should be probably better discussed in another bug.)
I can confirm that Timothys Hack with downgrading the mentioned packages is a working workaround for the kwin crash issue (no more crashes when resizing the window etc. as well. (Unfortunately it does not tackle the performance issue in QT applications which I hoped was correlated with this problem but should be probably better discussed in another bug.)