Unit Tests project stops getting compiled by MSBuild upon moving the solution file

Unit Tests project stops getting compiled by MSBuild upon moving the
solution file

I have a MVC 4 solution and I need to move my solution file from its
existing location to its parent. I selected the file in the "Solution
Explorer" and did "File->Save As" and browsed to the parent folder and
saved a copy. When I open up the .sln file in Notepad I see that the
project refs were correctly updated to point to the new location of the
projects with respect to the solution. Now when I build my solution there
is no "*.Tests.dll" file for my test project being generated in my Startup
Project's bin folder. I "Save As" again back to the old location and the
dll gets generated just fine. Is there anything I am missing here? Is this
the wrong way to move a solution file?
I am using MSBuild to build my solution and run it from Powershell
pointing it to the solution file.