This is already cross-posted at MS Connect:

https://connect.microsoft.com/VisualStudio/feedback/details/560451

I am attempting to override the property $(MSBuildExtensionsPath) when building a solution containing a C# web application project via msbuild. I am doing this because a web application csproj file imports the file "$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v9.0\WebApplications\Microsoft.WebApplication.targets". This file is installed by Visual Studio to the standard $(MSBuildExtensionsPath) location (C:\Program Files\MSBuild). I would like to eliminate the dependency on this file being installed on the machine (I would like to keep my build servers as "clean" as possible). In order to do this, I would like to include the Microsoft.WebApplication.targets in source control with my project, and then override $(MSBuildExtensionsPath) so that the csproj will import this included version of Microsoft.WebApplication.targets. This approach allows me to remove the dependency without requiring me to manually modify the web application csproj file.

This scheme works fine when I build my solution file from the command line, supplying the custom value of $(MSBuildExtensionsPath) at the command line to msbuild via the /p flag. However, if I attempt to build the solution using the MSBuild task in a custom msbuild project file (overriding MSBuildExtensionsPath using the "Properties" attribute), it fails because the web app csproj file is attempting to import the Microsoft.WebApplication.targets from the "standard" Microsoft.WebApplication.targets location (C:\Program Files\MSBuild). Notably, if I run msbuild using the "Exec" task in my custom project file, it works. Even more notably, the FIRST time I run the build using the "MSBuild" task AFTER I have run the build using the "EXEC" task (or directly from the command line), the build works.

Has anyone seen behavior like this before? Am I crazy? Is anyone aware of the root cause of this problem, a possible workaround, or whether this is a legitimate bug in MSBuild?