I've come across a very weird thing while mapping with MV.
Whenever I place a piece of tilesets that overlap with another, it all gets out of place and messed up when I test the game.
I thought it was a plugin doing this somehow, so I made a new project and copy-pasted one of the maps with the problem.
Well... it didn't solve much.
Then I made a completely new map and tried two things:
1 Placed a piece with no other pieces (save for the grass) underneath.
2. Made the same piece but with another underneath.
This is the result:
And this is how my map looks like in the game:
Finally, how it looks in the editor:
I definitely think It's an overlap problem and cleaning up what's under the current tile resolves the problem, but It's a bit annoying.