If anyone's interested, the workaround is to set the admin environment to 'dev'.
It's got to do with the Requirements::combine_files function. For some reason SS does that in live, but not in dev.
I just recently fixed an issue related to that this week. Are you on the latest version?
Ah, that makes sense!
I tested using the latest version of DOM, but ultimately left the version I delivered to the client which is about 3-4 revisions back from HEAD I think.
Was the change in DOM or Image Gallery (or both)?
I'll certainly update to HEAD if you've got a fix in.