Since installing Dawnguard (PC version), I've twice had a dead dragon simply appear near me out of nowhere, and I got to absorb its soul. There was no dragon attack at the time. Free dragon souls are handy, but this is weird. I never had this glitch in my prior 200+ hours of playing the game.

One time was in Solitude as I walked toward Proudspire Manor. I heard a fire sound and looked around for its source. I got the dragon soul absorption swirl of colors around me. I discovered a dragon skeleton clipped into the back wall of Proudspire, hanging out onto the bard college porch. A crowd gathered and commented on it as if I had defeated it. I went inside Proudspire and came out later. The dragon corpse now had its skin and muscles back on and was lying more fully out on the porch.

The other time of instant dragon corpse was at Dragonbridge during one of the random enemy attacks. Serana glitched as well during this combat, getting stuck casting a spell forever. After the combat, I noticed the dragon soul absorption and looked around to see a dragon skeleton lying on the road some distance behind me.

Both of these happened shortly after I fast-traveled.

Yep it happened to me too. His body still lingers inside Whiterun. Is annoying.