Picking an item in the inventory or in a chest by clicking it does not work

To pick any item from my inventory or a chest I cannot just click on it, I instead have to hold and drag it. Also shift-clicking does not work.

When I drag the item from one spot to another in the inventory, the quantity of items I am holding is displayed above the item sprite instead of below it.

If I am dragging more than one item it tends to spread itself across the inventory spots.