Technical Information
Double Hotbar version: 1.3.0 (encounter); 1.3.1 (reproduce)
Minecraft version: 1.19.4 (encounter); 1.20.1 (reproduce)
Other mods (if relevant): hundreds of mods (1.19.4); fabric api 0.90.0 and cloth config 11.1.106 only (1.20.1)

Describe the bug
After picking an item from the upper bar to the hand in creative mode, if the slot under where that item was has been filled, swapping hotbar places an extra item in that slot as if that item hasn't been picked.

Expected behavior
That slot becomes empty.

Steps to reproduce

Enter creative mode.

Place a block in the upper bar and another item under it.

Pick a same block.

Swap hotbar.

Additional information
If the lower bar is full, the item which has been in the hand is swapped to the upper bar upon picking the block, and disappears upon swapping.