Just wanted to add my experience here. Like the rest of you, I just ran into this issue with all sorts of weird behaviour as others have found.
I think you are jumping the gun to blame Mikrotik here. You know what else has had a lot of updates in recent months apart from RouterOS? Notepad has.
As much as I don’t really use Notepad++, I just switched to it and the problems instantly went away.
Now I can’t say for sure that is isn’t a weird Winbox compatibility issue, but I do know for a fact that Notepad has had a tonne of updates (which I’m personally not a fan of, but that’s a different issue) so at least for now just switch to Notepad++ when doing this kind of task.