Hello. There seems to be a bug with the Visual Studio 2012 C++ debugger.
When a project's Property Pages -> Configuration Properties -> Debugging -> Environment setting is used to update the PATH via PATH=NewPath\;%PATH%, the updated path is not available in the debugee.
I have carefully looked through forums, and this is a known issue from the past that has supposedly been fixed (see https://connect.microsoft.com/VisualStudio/feedback/details/695051/debugging-environment-variable-not-working).
However, the problem currently exists in Visual Studio 2012 as of July 17, 2013.
I cannot find any current discussion of the issue.