Minecraft 1.20.1 (Fabric 0.15.9)
inmis-2.7.2-1.20.1

To reproduce:

1. Open inventory

2. Equip a backpack

3. Click an item in the inventory/hotbar to "hold" on to it with your mouse

4. Click the backpack tab with the held item (in this case, a slab on a gilded backpack) as shown:
   

5. Item disappears when backpack GUI is opened

   • The mouse is also reset to the center of the screen, which can be quite jarring
     

6. The item does reappear upon closing the backpack tab and opening the inventory again (with the mouse holding on to it)

   • But only the inventory, item does not reappear if the backpack is opened.

Expected behaviour:
- Mouse continues to hold on to item, after clicking and accessing the backpack tab, allowing for easy placement into the backpack
- Mouse also retains its previous position at the backpack slot

Proposed UI fallbacks:

• Provide a configuration option to remove the backpack tab (or at least make it unclickable) while the inventory GUI is opened. Backpack can only be accessed via hotkey B (and when inventory is closed).