Tracked this down to commit 906a2d1 being responsible. As this commit was just some refactoring in preparation for (unsuccessful) attempts at improving rendering issues, I've fixed this simply by reverting it, and the fix will be included in the next build. Making this post just so people are aware it's a known issue.
This probably also applies to other cases where "wall" graphics (or in Loap terms, overlays) are used, rather than being specific to the Fun 8 effect, but that's the most noticable case of it.
