Mounting works just fine for me from Bear, Cat, travel, and even aquatic form. Maybe it was stealth-hotfixed yesterday?
Funny thing, I opened my mount tab to try both clicking from the book and hitting a bar key. I don't have a level 40 mount. I must have waited all the way to level 60 back when BC first came out before I paid for riding training. I think it was the running all over Hellfire at +40% travel form that convinced me a mount was a good investment.