This is not a perma bug but you can use it for a short while, to escape from allys/horde sometimes, do this:
1.Use the ability/spell "Sprint"
2.Mount up your normal "RIDING MOUNT" not flying.
It works with epic too.
3.Then u got sprint on mount and run over 100% speed for 15 secs.
NOTE: This doesnt work at all ASCENT servers. Maybe works at MaNGOS.
Enjoy