Riding on your mount, hitting ‘1’ (doing the attack from your mount) or ‘Right-click’ (dismounting), triggers whatever ability is set to your character, on those keybinds.
Currently I have ‘Unstable Current’ on my right-click, and if I dismount using right-click; it uses ‘Unstable Current’ (unless it’s somewhere an ability can’t be used - like in a hub).
This goes for most things on the ‘1’-key as well. Seems to only do it with “instant casts”.
I’ve had this happen on both Barb (where it does a shout ability, because they’re bound to those) and Sorc so far, so it’s not exclusive to Sorc.