The bug:

When you double click an item in your inventory in the same slot, the first click is normal but the second click doesn't put it back in the same slot.

This is very likely because double-clicking attempts to mass accumulate items in your inventory of the same type to your mouse cursor.

Steps to Reproduce:

1. Place an item in your inventory.
2. Double-click on it with the mouse cursor in an attempt to hold it with the mouse cursor and place it back in its slot in quick succession.
3. Notice how you continue hold the item with your mouse cursor and it doesn't get placed back in its slot.

Video:

Here's a video demonstrating the bug:

https://youtu.be/-Fqtmx0R8as