Looks like it's another bug. I'm sorry that you're finding all these bugs, but I'm also happy that you're finding them so we can fix them!

On the plus side, it was an easy fix - I've got it working locally and it will be in version 3.2.

Thanks!

I know there are more problems with the TextSprite editor for isometric objects (e.g. the color pickers don't really work) - it's just not a very common thing to use isometric text sprites so it wasn't really tested much. Now I've noticed these problems, I'll see what I can do for the next version.