Keypresses not detected in saved configurations (Ubuntu Mate 18.04.5 reinstall)

[granric]

Had to reinstall a machine with UM 18.04.5 from its .iso and, since then, editing rules is largely compromised: when in the Renamer tab, I can click within each box and position the cursor, but keypresses are no longer detected (can't move with arrow keys, can't add or delete characters). Weirder than that, I can define new rules (and - as long as I stay within the new rule - keyboard works as it should; but as soon as I exit the rule, and return after having clicked elsewhere or having added another one, that same new rule cannot be edited anymore).

However, rename operations, as well as deleting existing rules and other mouse-driven actions, work as intended.

Presently on metamorphose2_0.9.0.beta-1sav0_all.deb, installed via Gdebi (obviously, no missing dependencies); fun thing is that until the reinstall (when I already was on UM 18.04.5, but coming from an upgrade path from 18.04.2) functioning was nominal.

Launched the program with -d parameter, no log whatsoever (neither in ~/.metamorphose, nor in /var/log); FWIW, permissions on all .cfg files are standard 644, file ownership is $USER, and iBus/keyboard configurations have no customizations.

Any suggestion on how to overcome this weirdness is greatly appreciated.