If there are more that one mock objects existing in the test, Mock.Assert wrongly succeeds while evaluating arrangements for each mock, but not the very first one. This is a regression compared to an older version from 2012. The following sample demonstrates the case:
public interface IFoo
{
    void Bar();
}

[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestMethod1()
    {
        var bar = Mock.Create<IFoo>();
        Mock.Arrange(() => bar.Bar()).OccursOnce();

        var foo = Mock.Create<IFoo>();
        Mock.Arrange(() => foo.Bar()).OccursOnce();

        Mock.Assert(foo); // Would wrongly succeed
        Mock.Assert(bar); // Would fail as expected
    }
}