I used to use GupPet until it started falling apart -- most people can't seem to reproduce this but it stops showing mount names correctly, would summon slow mounts instead of fast ones (before normalization, this was a problem) and would often summon ground mounts instead of flying ones (still a problem if I'm in flying-enabled zones and want to fly).

I saw one or two corroborating reports of the same, saw no suggestions other than "clear your cache", and kept having the same problem even after I cleared the cache.

I switched to RandomCompanion, which does exactly what GupPet does. The UI isn't quite as nice, but it does the job and it does it right, so until whatever broke GupPet (maybe another addon, who knows?) is fixed, or until I decide to bother to try again, RandomCompanion works fine for me. The only thing I still need to do is figure out how to get it to summon a ground mount if I hit Shift+F1 in a zone that allows flying, so that I'll be able to stay grounded if I want to in Azeroth once flying is enabled there. (F1 currently calls a random mount).