I put a few buried treasure maps into a chest since I didn't want to go find it right away. When I came back yesterday, it had turned into a regular map. I don't have a screenshot of what the map looked like before, but right now it just shows my base.
Is this still an issue in the most recent versions (currently that is 1.15, or the latest pre-release 1.15.1-pre1) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.