I just left the PTS server and could not get Rapid Maneuver to work anymore while mounted in PvE areas. It works while unmounted, but not mounted- it would 'appear' to work, I'd get the glowing yellow, but my speed would not increase at all.
Also, I did notice that sometimes the yellow would appear, sometimes not, but no matter which, I was still charged for the Stamina usage.
CP: 1965 ** ESO+ Gold Road ** ~~ Stamina Arcanist ~~ Magicka Warden ~~ Magicka Templar ~~ ***** Strictly a solo PvE quester *****