Game hard crashes when casting some spells of a too-high level

[comradeshook]

As per title, if you use e.g. cheat spells 6 in console and attempt to cast Fireball, the game immediately crashes to desktop. Some other spells work or don't work, but finding a pattern is difficult. Specifically, Lesser Heal seems to work while Missiles of Magic says you have too many missiles active to cast it, whether or not you actually managed to cast it beforehand.

Playing on Windows, GOG version, v1.9.0 alpha12. (... same story as usual, figure it might be relevant for archival)