OK, that seems to have fixed it.
Turns out Rabbyt caches textures internally, so just reloading the images for my sprites didn’t make any difference.
A little bit of digging around in the source and I managed to work out how to empty the texture cache. Once that was done I just had to refresh the textures for anything already existing and everything was happy again.
Of course, now I’ve found a new problem. All my sound effects seem to be playing about 0.5 seconds out of sync with the game. Grr…
EDIT : OK, that was easy enough. Just needed to bump up the buffer size a little.