Customizing map texture may appear on other worlds:

If I'm playing in a custom world, exiting it and opening another world may have parts of the custom world's texture on a default map. This bug was only tested on official maps and the texture change was very subtle being in the selection of items. I'll put an arrow on one of the images to better highlight the texture change.

Nota: I don't know if it can also happen with mods made by the community.

Map that was used for testing: Spellrune (available for free on the marketplace).