Okay, this is really annoying. This is a fresh copy of WoW, just downloaded it.
Every time I restart the Launcher (e.g.: quit from game and start it again), it starts to download everything from the "Available" part.
So, after every restart, I have 5.6gb to re-download. Not really convenient with cable.
(I tried the repair tool, but it only checked the wow.exe and said everything is OK.)
Best Answer
It turns out, that installer will report you that the game is downloaded, everything is fine.
But after your first login (and log out), it will start downloading, again.
I think this is due to the Cataclysm/WoTLK content which some of the people may not have.
But that's only a simple assumption. So if it starts downloading again, let it download. It can do it in-game, but it needs some speedy net connection for that.