The following spells all have something in common:
in a swamp level, they will all crash the game when the targeting cursor moves to a certain positions on the map. It was reproducible by moving vertically and the crash tiles would still be in the same relative position from the player, and only for those spells (tested all targetable spells in the common, air, earth, fire, water, and druid schools at or below the circle of hurricane). Moving horizontally did shift the relative position of the crash tiles.
I suspect it could occur on other wrapping special levels as well, as it was not tied to a particular map tile but rather a position relative to the player's current position. Also notable that the targeting itself was the crash trigger, I was not having to confirm the casting of the spells. All of these spells are capable of modifying tile contents in some way, that seems a likely culprit.