A few days ago ransroth wrote about new feature which was added after Mounts 2.0 system was written. This feature has resolved the bug that was discovered by Beta Testers, as a keyboard shortcut in the Options panel.
There’s a new Keyboard Shortcut called “Dismount/Remount”. When used by a mounted player, that player will be dismounted. When used by an unmounted player, that player will attempt to mount up on the last successfully-used mount.