Digging into this is a bit interesting. It looks like we end up with the validation in two different locations - one from the RequiredAttribute that we added as part of this changeset and one as a consequence of this check - https://github.com/aspnet/Mvc/blob/dev/src/Microsoft.AspNet.Mvc.ModelBinding/Binders/MutableObjectModelBinder.cs#L288

I think having the one in the DataAnnotations should suffice and we should be able to safely remove the other check.

@GrabYourPitchforks might have more context about this. I can bother him tomorrow when he gets in and see what he thinks.