Serious graphics lag e.g. when dragging windows

Hi all!

I just upgraded from 42.2 (online dup) to 42.3 and everything went fine. But now I have a very slow reacting screen: when I hold the mouse button down and move a window on the screen the full window follows time lapsed with appr 1 inch distance on screen when moving fast (and keeps following former mouse movements for appr 1 second after release). With 42.2 everything was OK.

To nail down the root cause I can provide the following additional observations:

  • Graphics card is a radeon HD 4200. glxgears is OK.
  • Full HD video is running fine and without significant CPU load (appr half a core of two) within VLC
  • the described lagging doesn’t produce a signifcant CPU load (maybe 25 %)
  • lagging can also be observed when e.g. panning a photo in darktable

What additional information do you need to get closer to the root of this problem?

Any help appreciated.

Thanks a lot