Switching from VS2010 to 2012, I found a different behavior with devenv command line.
devenv mysolution.sln /build "Release" /project myproject was successful with VS2010 (using the name of the project instead of the path).
With VS2012's devenv, I had to specify the full or relative path to the project: /project "somedir/myproject/myproject.vcxproj" to make it work.
Note that the projects in my solution are still compiling with VS2010 versions of the compilers
VS2012 documentation does not specify that both projects name and path can be used, so maybe it's "as designed". In this case, please consider my comment as a feature request :-)