This is a bug that is as old as flying itself. When you are on your flying mount, hit your spacebar to go straight up. Hit your forward arrow key to go straight forward. Notice that the mount aims you 30 degrees down until you finally hit the ground instead of flying straight ahead. Maybe someday this can be fixed (shouldn’t be very hard really) and we don’t have to see people flying around as if their mounts have had too much of the dwarven stout. As a player, this makes me feel drunk sometimes. It’s not fun.
The reason this is a problem? Do a quest that requires you tilt the camera toward the ground to look for items/npcs/etc… You cannot maintain altitude without constant fidgeting… doing this for a long time can make a person queesy.