Steps to reproduce the behavior:

1. Acquire a backpack and put an item in it. The tooltip says 1 / 27.
2. Select the backpack in your hotbar and open it.
3. Observe that the tooltip says 0 / 27, despite there being stuff in the backpack.

Versions:

• CCL: 1.16.5-4.0.7.445
• CB Multipart: 1.16.5-3.0.4.123
• ProjectRed: 1.16.5-4.13.0-beta-28

This has to do with duplication protection, where the backpack is actually emptied while the GUI is open. Previously, contents were re-saved to the item when the GUI was closed, which allowed various exploits to remove items from the bags without saving the removals to the item.

Will fix by simply removing the tooltip while backpack is open.

Addressed in ac82ead