Maybe you installed it in a different drive or folder, and instead of upgrading, it just installed a different copy, and the link led to the old copy...
In any case, there is so little difference between the two versions. It really doesn't matter anyway.
I have just downloaded (& installed)version 1.06, but the build is still showing as 1.05. Confused, to say the least. Anyone else have the same problem, or is it a glich?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic