The middle mouse is indeed a pain. I use the right-click-to-steer method of moving, configure button 3 (middle) as 'forward' and button 4 as 'auto-run. If I click B4 and start running, then right-click to steer I'll often accidentally hit B3 and run in a straight line as the steering doesn't happen: trying to press B3 and then steer never works.

I configure the mouse in the same way in all games I play but only in XIV does this steering problem happen.

It's not SE's 'fault' per se as it's hard to call it a 'bug', but it would be nice if the middle button didn't interfere with the operation of the right button.