Holding down Shift + Tab doesn't allow to select Slot 1 with keyboard

When a player is holding down both the sneak key (Shift) and players list in multiplayer (Tab), it is not possible to select Slot 1 with keyboard (press 1).

This is not a hardware issue with keyboard. The same action worked successfully in Minecraft 1.8.8.

It is a common scenario in multiplayer PVP games like UHC.