When you finish your upgrade to SP1 do not forget to navigate to:

1. In the Configuration Manager console, navigate to System Center Configuration Manager / Site Database / Site Management / <site code> – <site name> / Site Settings / Client Installation Methods
2. Right-click Software Update Point Client Installation, and click Properties.

As soon as the properties window opens you will be notified that the published version is not the newest.  Your choices will be to ignore or to upgrade.  Simple, but you have to do it.

Old Version:               4.00.5931.0001

Available Version:      4.00.6221.1000