I'm experiencing the same problem since I updated my application from Angular 1.4 to 1.5.2.
Whenever my tests hit a $scope.$apply() or $httpBackend.flush(), the default route ('/') is resolved and it tries to fetch its data from the backend. In my case, this route has a 'resolve' property that calls a rest service before trying to load the template. If I comment out the 'resolve', then it tries to fetch the route template. Since my tests don't specify those http expectations, those tests fail.
I've managed to work around this issue by segregating the route config in another file and excluding it in my karma.conf.js config file, but I'd rather not have to do it. I'm still searching for a better (right?) way to do it, but no luck so far.