Difficult inventory management

Whenever I go to move anything in my inventory, I have to click and drag it to move it anywhere. Shift-clicking doesn't work, and I can't pick it up normally. When I have to drag it it shifts the sprites to an odd location and it will occasionally drop an item into an open slot it moves over (for example, moving a stack of cobblestone over an empty slot sometimes drops 1 cobblestone there). Additionally, when I go to drop an item into a slot, it disappears only to reappear in the initial stack once I place it in a slot.