Placing a sign and then having it broken while in the GUI doesn't automatically close it. For example, if you place a sign on the face of a BUDded piston and it retracts, the GUI stays open.
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Avoma
violine1101
Thank you for your report!
We're tracking this issue in MC-117815, so this ticket is being resolved and linked as a duplicate.
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Duplicate of MC-117815.