I am aware that this situation can be resolved by *not* having WoW recognize the extra buttons and instead using a special driver that treats the extra buttons as keyboard strokes (say ALT+F1 through ALT+F9 or something), and then, for my initial example, assigning one of those key strokes to "Action Button 1" instead of a mouse click.
However, it seems like it ought to be possible to resolve this in-game. A UI option to only act like I left-clicked if I actually left-clicked, for example. Is this option available (am I missing it)? If not, do we know whether this is considered to be working as intended? It's not clear to me what the value is of having WoW recognize the extra buttons if it causes this trouble.
Any help would be appreciated.