Pre-build MSBuild task to update AssemblyInfo not in sync with built exe

I am using a pre-build task in Visual Studio 2008 that invokes msbuild:

C:\WINDOWS\Microsoft.NET\Framework\v3.5\MSBuild.exe $(MSBuildProjectDirectory)\version.targets /p:Configuration=$(ConfigurationName)

Inside version.targets, I am updating the AssemblyInfo.cs file to replace version information:

   <FileUpdate
        Encoding="ASCII"
        Files="$(MSBuildProjectDirectory)\Properties\AssemblyInfo.cs"
        Regex="AssemblyInformationalVersion\(&quot;.*&quot;\)\]" 
        ReplacementText="AssemblyInformationalVersion(&quot;Product $(ConfigurationString) ($(buildDate))&quot;)]"
    />

When I build the project through Visual Studio 2008, it builds without any problems.

But when I look at the resulting exe's version information, it contains the previous time stamp even though the AssemblyInfo.cs has been changed with the "correct" one.

It seems that the pre-build's changes aren't seen by the main compilation task and it's always one behind.

Any ideas of what I'm doing wrong?