Client mod not disabled fully on servers without the mod.

[kasamikona]

When connecting to a server with no support for this mod, as expected, it will show "[Multi-Hotbar] Multi-Hotbar Core is not installed on the currently connected server. All Multi-Hotbar functions will be disabled."
However, using 'pick block' (default middle mouse button action) with a full hotbar still attempts to put the item in an extended hotbar slot and switch to it.
On the server I visit most often, this results in an immediate kick for "Invalid hotbar selection (Hacking?)".