I've purchased a flying mount (wings) but holding down the space bar doesn't initiate flight. I've checked the control/movement options...set for spacebar.
Is there a special trick to get the flight wings to work with ProfitUI?
There shouldn't be, since it's not a UI function. I use the "move up" key. Space bar is just jumping, which if you jump from the ground should put you back on the ground.
if you placed the wings in your used mount slot be sure to dismount and remount, or you will be getting the benefits from and still using the original mount.