Obviously, this is a multiplayer only bug, of what I have seen. But, If you walk and hold down tab, you can't switch to the 1 & 2 slots of your inventory using the number line. Only mouse wheel. Not sure if intended, but it's something that I don't thing is correct.
Linked issues
Comments 3
Yes, maybe it's my keyboard or something.... what are you using, windows? mac?
And Also, It's probably only going to work on a server, so make sure you are using one.
Are you sure? Tested and can't reproduce.