I noticed that u can throw away items faster when you hold Q. I did this and then switched to a other slot trough pressing the hot key (1). but insead of also throwing out the items one after the other, one item of the stack (64) in slot 1 got missing (now 63) (it wasn't on the floor). the then I pressed Q again an item landed on the floor and the number in the indes of the items turned to 62 and quikly back to 63.
steps to reproduce
1. put one item in slot 1
2. go into a diffrent slot press Q for at least one second
3. then while still holding Q press 1 (to switch into slot 1).
you will see that as the cursor goes to slot 1 the item disapears.
its not actually gone its just invisible. as you can see the item will be revealed when pressing Q again.