If you try to fly to Ghostlands, or Silvermoon from Undercity, or any other flight path through the Eastern Plaguelands you will be dissapointed, since the flight path is broken. As soon as you enter the Eastern Plaguelands you'll see the loading screen, the mount underneath you will disappear, and you'll drop on the ground.

I bet the same will happen if you try to fly from ghostlands to any other southern location through eastern plaguelands.

Can it be fixed anyhow?

And I've encountered this issue when I've decided to fly to the booty bay through the entire continent from the silvermoon.