Yes the same without any mods at all, I did put that in original post.
File link - https://we.tl/t-B0d38v1wk8
Just loaded my 14.4 backup and this is what it looks like. So it must have occurred during the switch. Do you still need the backup adding? it's 317MB. And it appears the undiscovered bits are clear - my bad, thought they were white but that's when you're holding them (still a bit of a noob).
[media]
I'm in 1.9 and just tossed another 1:16 map in the lava, cuz I forgot to put it away before going through the nether.
I didn't realise it had done this until I'd done a good few hours work on my slime farm and I don't want to do that again so I haven't restored to it. It's not many maps, I can sort it out. I was more concerned for those with massive map walls who may not have updated yet. Might be something I did , if it's not done that for you then it's likely either user error at my end with maybe updating with mods on or something . Everything else is working fine and I'm happy with what's going on elsewhere. Thanks for the quick responses. Sorry to be a pain.