Arch recently upgraded to 5.12 and there are now a lot of reports arising from Krita crashing with pen devices immediately upon touching a canvas with one.

With a bit of blaming I tracked it down to commit d2e0e416d4444ccf3c208d6770e32ff0fb04b543 as the only change between 5.11 and 5.12 that could cause this. When I rebuilt after reverting it this bug goes away and Krita works fine on 5.12.

This happens on the stable releases of Krita and Qt, all the way up through master and dev branches respectively and doesn't happen on 5.11 (ie, before this explicit delete commit).