the undiggable tiles i have no idea why that happens, but if you just flag and unflag them it fixes it. (also placing flags on coils, i have not played enough normal MS+ and looked a 11 to notice anything.)
its diamond thats why the background is cyan, and it's not squished because its still fits in the same 16x16 box as the other ones. but i could compress it a bit in the next update.