This seems extremely confusing, I almost restarted the process and I'm sure a lot of players that might think "it doesn't work" haven't noticed it:

The game if started for the first time today may start to do the "optimization of disk space" that is new in 4.3.2.

However, the whole window informing you of that may not be there at all after the first few seconds.

Starting wow.exe re-shows the window and it seems more promising.

I don't have a problem (yet?), just informing you, this seems quite confusing.