If you place any wall block (I've tested them all) between 2 blocks along the X-axis, the 'up' tag will be set to on, whereas if you were to rotate this setup 90 degrees (in between 2 blocks in the Z-axis) it will not be.
After updating the block with 'up' tag by placing and removing a block next to it it gets reverted to being without 'up' tag.
I hope this explains it, if not watch the video I provided 🙂
Thank you for your report!
We're actually already tracking this issue in MC-171023, 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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