Visual Studio 2015 new files not being added to source control automatically

Question

I have just upgraded to VS2015 and I am experiencing an issue I have not seen before. Using an existing solution under source control, I am able to modify files and they get

Answer 1

We were also experiencing this issue but in our case it was because we had folders that ended in ".Lib". Figured it out from this SO question: Visual Studio 2015. Files not added to TFS