Standard behavior: When levitated up in the air, you can move in a downward direction by simply facing downward while moving forward, or upward while moving backward. This same ability for mounts was patched into EQ some time after mounts were introduced (originally they could not do that.) Bug: Except Drogmor mounts don't work right. Using a Glowing Black Drum mount, you cannot move in a downward direction by facing downward while going forward. Conversely, moving backward, you always float drastically downward no matter what your view's vertical orientation is. Not sure if this is related to the other view orientation/mount bug I will post.
I reported this drogmor irregularity a few years ago. As I recall, I ended up exchanging PMs with Prathun who said all mounts navigate the same way, the drogmor shouldn't be doing anything special or different. However. it does.
Ghostrider's Bridle / Ghostrider's Spirit mount still have this problem. I picked up the bridle this week on Thornblade and just discovered the inability to use first person look down to levitate downward. The END key on the keyboard still works.