Created attachment 122677 [details]
Example of freezing when moving a selection by a selection tool

SUMMARY
Trying to move a selection by selection tools(a selection itself but not it's content) in 4.2.6 causing freezing of the entire desktop while dragging. I.e. when you start to drag a selection by it's border the windows(not only the krita window but every open window that has some visual activity going on, like system monitor for example) stop updating until the move is over.



STEPS TO REPRODUCE
1. create a new file.
2. Make a selection by box selection tool
3. Try to quickly move it by it's border(like in circles or something like that)


OBSERVED RESULT
Everything but the mouse freezes.


EXPECTED RESULT
No freezes both in the krita window and any other window as well.


I've attached the video showing how it looks on my system. Moreover i've done some digging with krita versions I have on disk and the results are:

4.1.7: the feature is not presented
4.2.2: no freezing(although a little laggy)
4.2.3: no freezing(although a little laggy)
4.2.5: freezing on move before the drag ends
4.2.6: freezing on move before the drag ends

My system is ubuntu 18.04, nvidia drivers 430.40, x11 server.