When I try to create a Levitate potion from Racer Plumes and Coda (Cada?) Flowers, the game insists that I rename the potion first or it won't create it... but when I try to rename it, it still won't finish the creation process. Any idea why?

This is a very common bug that can happen to any potion.
Luckily, the http://morrowind.nexusmods.com/mods/19510 has a fix for it. (among many other great game fixes)