Searched for this before and nothings came up,
Basically its just a minor Mount Exploit, on the server im on we also get that DND+ Mount Speed buff so we run at 300% Speed instead of 100% which is kinda useful.
What you need:
The person you want to dismount bug.
A Hunter.
A duel or Gurubashi.
Basically mount up, get the hunter to duel you and then get the hunter to use distracting shot on you only.
And Voila, No mount visual, Watch out tho, ppl will report you to GM's.
Have fun.