Crashing when removing Modifiers

[Ceroce]

In the Keyboard Layout editing window, under the Modifiers tab, removing a Modifier from the table view almost always makes the application crash on my Mac (under Catalina).

[eugenesvk]

I have the opposite – it crashes only when I add a modifier, but only when I copy some other modifier (linked or unlinked) with version 3.5.4 (was fine before the update, I managed to copy a few modifiers earlier, but now it crashes every time even on an empty keyboard), also Catalina
If I just add/remove, no crashes

Can confirm that the other latest download – v3.4.2 – doesn't crash on the same operations