I kinda had the same problem when I added H as a healing(Healer A) macro and shift+H (HeALER b)as a secondary healing macro for another char.

When I pressed H, the macro for the first healer worked just fine, but when I pressed Shift + H, both chars began casting a heal.

I fixed this by binding shift+H (=Healer A)to an empty button spot for the first healer.



Works great for me and might fix it for you .. ?

PS: I use the Bongos addon for my buttons and bindings, you should too, never use those bars again