Only affects bindings not using unit frame targets.

Creating a binding for a mouse button and adding a modifier (e.g. shift + mouse button 3) doesn't work when hovering over a unit frame when the target condition has been set to regular "Binding Targets".

It works fine when the "Unit Frame Target" is enabled, or when not hovering over a unit frame.

This seems to be a WoW bug as the same issue can be seen when not using Clicked, however that also impacts unmodified mouse buttons.

The above configuration will work fine when pressed while not hovering over a unit frame, but as soon as you press mouse button 4 when hovering over the player frame (or any other frame) it will reject all input.

No addons enabled:

Added a message in the interface advising people to enable the "Unit Frame Target" when working with a Mouseover target and a mouse button. Additionally I removed the mouse click registration from the macro frame handler, so unmodified mouse buttons will not work anymore either, mainly to maintain consistency.