Today my lowbie monk was at Wyrmrest Temple, and after some chitchat with Alexstrasza, she tried to summon her mount and fly away. Alas, she got the “Ground mounts are not allowed here” error.
Talked to Torastrasz to send me down to ground level, attempted to summon mount again. Still not allowed.
Hoofed it to the FP, then took the taxi to Fordragon Hold. Attempted to mount up to ride up to Bolvar. Still not allowed. This error is following me, it seems.
Hoofed it to Bolvar, completed the Wrathgate thing. Attempted to hearth back to Wintergarde Keep, but it would seem that Alex’s pacification of my violent tendencies also stops hearthstones from working. That’s a different issue, though.
Hoofed it back down to the Fordragon Hold flight point (because still couldn’t summon a mount), took the taxi back to Wintergarde. Where I still couldn’t summon a mount.
The only way to clear this error/prohibition is to completely log out and log back in.