This has happened to me too. not every time but enough to be annoying.
it was hilarious the first time…the following attempts to get back to stormwind makes me think that their Horde bias is enjoying drowning the blue crew.
Came here to report the same thing. So far a SW portal has sent me to 1) below Arathi Highlands in the water where I am losing breath and fatigue. 2) to the Isle of Gilneas and 3) out to the sea of Twilight Highlands in the water again losing fatigue. Each time I re-cast Mage portal Stormwind and end up in the correct Portal Room in Stormwind. Has a Goblin transporter been messing around with our portals and it’s “pot luck” where we end up???