This bug has a very low reproduction rate, maybe one time in 20, if that.
The symptoms are that I’ll switch to SkyRiding, use that to reach my destination, and then when I try to switch back to Steady, I click on the Switch Flight Style button in my action bar, and I get the error “Spell Not Learned”. Once I get stuck like this, the only way to switch back is to log out and back in again.
I don’t have any better reproduction steps than what I’ve been able to provide, such as a a flight that regularly produces this, it just happens when it decides to. So it’ll take a lot of patience to get reproduction. Once it’s happening, then you’re good to go because it’ll continue to happen indefinitely, until you log out.