I posted ad-nauseam about this in the last build. Couldn't understand why more folks weren't affected.
AND, the slow syncing of 2+ years of texting coincided with the messaging app draining the battery on my 1520.
It finally caught up. About 3 days. Battery returned to normal and 10549 settled in nicely.
Loaded this new build on a 640, just to avoid messing up the sweet running 1520.
Ironically, the messaging app synced much quicker, and without battery drama.
Still, I'm loving the new functionality of the messaging app. Folding in Skype, and soon texting from desktop........
These current snags are the price for what I believe is going to be a fantastic new messaging experience.