Why does the Deployment Workbench show version 4.1 after installing MDT 2008 Update 1?

We've received several questions over the past few days regarding the Help, About Microsoft Deployment Workbench showing 4.1 even after the upgrade to MDT 2008 Update 1:

The reason why the Help, About Microsoft Deployment Workbench shows Version 4.1 is due to caching that can occur with certain DLL's.  In this case the value of the previous installation of that screen can be found here:

HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\MuiCache\@C:\Program Files\Microsoft Deployment Toolkit\Bin\Microsoft.BDD.WorkbenchResources.dll,-105

If you previously had MDT 2008 installed the value was cached in this location and unfortunately does not update properly after the installation of MDT 2008 Update 1.

So how do you determine if you have the correct version installed?  The correct version of MDT 2008 Update 1 is 4.2.523.40.  This can be found by going into Add/Remove Programs.  You should see an entry like the following:

If the About window really bothers you, you can delete the registry entry mentioned above and it will then update with the correct version number. :)