A few days ago, I've been facing a strange behavior with Visual Studio 2013.

No matter what solution I was opening, Visual Studio kept switching the source control plugin to Git. I was sure all my solutions were bound to TFS.

I didn't understand why Visual Studio was insisting. And when looking for a solution on stackoverflow, every single post were talking about switching or disabling the source control plugin in Tools > Options > Source Control > Plug-in Selection, or saying it was due to the hidden .git folder in the solution folder.

But there were no .git folder in my solution, nor in the direct parent folder. And Visual Studio kept changing back the source control to Git.

I finally found that it was my fault (who said of course? :-)).

The solution was located in :
C:\Users\Renaud\Documents\TFS\MyOrganisation\MySolution\

And actually, I finally found there was a .git folder in :
C:\Users\Renaud\
It wasn't supposed to be there, and probably resulted from a wrong command that I wrote earlier. That's why I had a hard time finding it...

So, it doesn't matter how deep is your solution... if any of the parent folders contain a .git folder, Visual Studio will assume every solutions contains in a subfolder is under Git source control. Just find it!