If a banner is broken by the player, it gets an NBT tag, even if it doesn't have a pattern on it. Then, if this "Null-NBT" banner is placed to the right of another banner in the inventory, it will assume the NBT data of the banner nearest it on the left. However, this "null-NBT" banner will not actually have the same NBT data as the banner on its left; it is only visual.
MC-63377
(Visual inventory) banners with NBT tag but no pattern clone the pattern of banner to the left in inventory row
Resolved
Incomplete
0
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.