When holding down 1 (hotbar slot 1) and then pressing and holding down 2 (hotbar slot 2) it will go back and forth between hotbar slot 1 and 2 a couple of times before landing on hotbar slot 2, instead of doing that immediately.

Steps to reproduce:

1: Hold down any hotbar slot key

2: Press and hold down any other hotbar slot key

Edit: This only works if the second hotbar slot that is pressed is to the right of the first hotbar slot.