When you and a player are behind a painting held by signs and he shifts, the nametag of the player shifting lets you see through the painting
Steps to reproduce:
1) place a painting on signs so you can go behind it
2) get another player behind the painting with you and make him shift
3) you can now see through the painting by looking at his nametag.
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Thank you for your report!
We're actually already tracking this issue in MC-162693, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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