Actually I wasn't able to reproduce it 100% neither -- still using the -3 build. Thinking whether it might is (cross-)related to something else. Braindump ;)
Currently I'm running a USB mouse and an USB keyboard via a USB hub -- this seems to work fine. When I was able to reproduce the error I was using a magic keyboard (Bluethooth) and an USB mouse. Mice are both budget ones -- but very classic ones (some Cherry model and some Logitech).
However, I will try to reproduce the issue with new build when I'm having access to the magic keyboard again -- will take a few days.