SUMMARY In the recent nightlies when user switches between two or more document the switch has delay and other issues. The major one is the layer thumbnails in the layer docker is regenerated every time the switch happens. This adds to a lag during the switch, the progress bar sometimes shows updating thumbnails. The user can't paint or colour pick during this slight registration time. STEPS TO REPRODUCE 1. Open the test files attached here in krita 2. Switch to subwindow mode in krita settings (don't know if this has any effect) 3. Ctrl tab to switch between these two documents. I am also providing a link to a video which shows how it behaves in my machine. https://box.raghukamath.com/cloud/index.php/s/4z2xe3Sx5g3owfC You can download both test files from here https://box.raghukamath.com/cloud/index.php/s/J3kQoF6SYfW3eLC
The bug should now be fixed in master! :)