Sign items with invalid JSON in Text1 tag are used in creative

When giving a player on creative mode a sign with the following command
/give @p sign 10 0 {BlockEntityTag:{Text1:"1"}}
the sign will act strange. This will only occur when the value for Text1 is invalid JSON.

Once you have the sign, just place it down and see the number of signs in the stack go down to 1 in the stack, then MC-105982 blocks it.

Other tags I have tried didn't result in the issue occurring.

Upon dropping the negative signs, you can't pick them up (as I would expect with the way picking up items is processed)

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Code analysis by Marcono1234 can be found in this comment.