Ok some have been reporting that being in Tazoon is causing them to 'fall out of the sky' and not be able to fly again.
Bit of testing on this and all i can say is this only happened to me when i was wearing a costume (Ancient zombie dragon) and it's not limited to Tazoon.
Wearing an costume (can only speak for Ancient ones) will cause 'random' no-fly zones all around Istaria.
Easiest to find thou is Port into Tazoon and try to fly straight to the Crater, you fall out of the sky just outside of Tazoon and cant fly again till your well clear of the area.