Filling in an empty map fills many blocks in with a stone texture where no stone exists. This issue persists across multiple maps, and at different zoom levels.
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Thank you for your report!
We're actually already tracking this issue in MC-179858, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in the latest development version of the game.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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