I fast traveled to Whiterun, and noticed a random dragon head sticking out of my house above the door. It was dead but not a skeleton. As I walked up to it I absorbed its soul. Well it makes nice decoration, at least until I fast travel back and I find it floating above my roof...

This happen to me too but I was heading to Riften and one fell out of the sky, there was another Dragon flying around so i just figured the argument didnt go so well for that one lol

I've killed Dragons in cities before and when I fast travel back to that city the skeletons are standing then they do this weird dance, then fall back down on the floor.

Oh the Skeletons have done that to me, they somehow moved closer to the building and start doing a humping type motion to the building

There's been one in Whiterun in front of the companions place, though it still has it's flesh and I can't absorb it. I've tried to shoot it over the wall with fireballs like I usually do in the towns but it seems heavier than it's skeleton counterpart. I think it's making the Whiterun framerate even worse, if that's even possible...

Okay, he's back. With his skin again too, though I can't absorb his dragon soul anymore... now he is dancing in the town square!!! He won't stop dancing, it looks hilarious. I think it's because he's stuck on one of the vendor stands.

try hitting it with the wabbajack staff XD

Well there is only 20 shouts in the game the player can get and 3 dragon souls for each word in the shout. Thats about 60 dragon souls your need to collect and thats without considering the free shouts you get from the Greybeards

One time a dragon turned into a skeleton before he was even dead. He was fighting me and a giant as a skeleton after I absorbed its soul.

Coincidentally I had just received the Blades blessing that gives you a critical damage bonus to fight dragons. I don't think the game was recognizing the correct damage I was dealing and therefore the dragon died before the game registered the dragon as dead. I noticed that even regular, crit damage is not being calculated/applied correctly.

Chalk it up as another bug they need to fix.