No invisible or backwards dragons here, but they have started crashing into scenery, which I never saw before. One in Riverwood was bouncing between trees like a pinball!
Completely normal skyrim dragon behavior. They will also fly headfirst into the ground and do a headstand before sliding away and flying off into the distance.
You may also find them half inside building flapping wildly to escape their man built tomb.
Don't forget that they also use wall hacks and are able to not only see you through walls but shoot you with their breath through them.
My dragons have been glitchy since day one. Not one flying completely backwards yet though.