Not sure how recently this disappeared - most likely with yesterday's big patch. But tonight I noticed that I am no longer able to get my legendary auras on my mounts anymore.
It used to be 100% reproducible: Draw weapons, then mount. Enjoy legendary auras/enrichments etc while mounted. Didn't work with every legendary though - I seem to recall being disappointed that I got no awesome green glow with Xiuquatl.
Frostfang, Claw of the Khan-Ur, and Howler no longer work while mounted.
People with other legendaries, have you noticed other legendaries affected?
To be honest, it was probably a bug to begin with, but I did consider posting this thread in the bugs section. Do you all think this is an intentional change?