Whenever you hit LSHIFT to dismout the plugin still thinks you are riding the pet..

Yup, it sure does. There's actually a little note about that in the 'Caveats' section of the download page. I'm still looking for a way to handle this, because realistically, I wouldn't have achieved a WASD Ride system without Mojang's addition of Horses (Bukkit doesn't allow listening to key presses).