I've had this issue for days now and it's driving me crazy.
I have two Macs, one I updated and it start to cause this to happen then I updated the next one yesterday and it's also happening.
I am using VS 2015 on Windows to develop (with a Mac build server).
The problem I am having is the storyboard (even in a new project) has started to auto size my controls when adding constraints to the same size as the old red outlined ghost shape that you used to get (sorry if that doesn't make sense). Some screen shots will explain it better.
Screen 1 - I have a view, I add a text box and I want to for example pin it's sides to the main view. So I am about to pin the right side (also why is the edge now inside the view?)
I pin the right side and almost immediately this happens. On my slower mac I can sometimes quickly pin the left side too before the view updates but I mean seriously that is not a solution. I can't resize it or anything now, just keeps reverting back to the same size until I remove the constraints again.
This isn't normal behavior is it? It's been a few months since I did iOS dev and I swear this didn't used to happen. All I can think of trying now is rolling back Xamarin on the mac to an earlier version as that did used to work This is a serious break in it's functionality. As in the storyboard editor is useless.