Why does Web Platform Installer not recognize that SP1 is already installed for VS2010?

I updated Microsoft Web Platform Installer (WPI) to v3.1 today in order to install MVC 3 Tools Update. I noticed that Visual Studio 2010 SP1 is not marked as "Installed", but I had a开发者_StackOverflowlready installed it via WPI last week. Does anyone know if this is a problem with WPI not recognizing and installed component, or if something has actually changed in SP1?

Additional Info:

I read another article that referenced this reg key as an indicator of the SP level:

Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DevDiv\vs\Servicing\10.0\procore

Value: SPName = SP1

Chris Sfanos (Web Platform Installer PM) writes on 04/20/2011 12:05AM in this Web Platform Installer-Thread under http://forums.iis.net/t/1177387.aspx: "I'll follow up with the VS SP1 team that owns the WebPI package for more details." Since then Chris gives no newer information, so it seems that Microsoft knows about the problems but has no remedy yet.