VS 2015 Update 1 - Claiming I am debugging a release build

Question

After updating to VS 2015 update 1, if I run a web project (MVC), stop the application, then try to run it again, VS stops and pops up a dialog claiming

Answer 1

There seem to be as many solutions as there are people having the problem, but in my case I had to remove and re-add a project reference. The project reference was in a unit test project in the same solution.