After contacting Bitwig customer support about a bug I was facing, they suggested that it was a bug in ibus: https://github.com/ibus/ibus/issues/2789.
Would it be safe for me to compile and install the latest version of ibus, or should I wait until the latest version becomes available upstream?
If you want the latest version, you can install the AUR package ibus-git.
This seems to fix the issue with the keyboard. However, now the mouse focus is only held shortly, when dragging vertically on a dial. Dragging horizontally, say, on the track volume works fine. The mouse seems to be more sensitive too. I suppose this is sometimes the catch, with having the latest software.
I’ll let Bitwig customer support know as well.