False positive "expression is always false" warning

I just upgraded to ReSharper 8 and I see this "expression is always false" warning quite a bit.  In 6.6 I was not seeing this so I would consider this a regression.  Here is an example on how to reproduce this bug:

        private bool flag;

        private void DoSomeWork()
        {
            flag = true;
        }

        private void Run()
        {
            if (flag)
            {
                return;
            }

            DoSomeWork();

            if (flag) // this is underlined as being always false, but as you can see, the DoSomeWork method changes it to true
            {
            }
        }

This seems like a dangerous problem because you could end up erroneously deleting code that ReSharper marked as unnecessary but this could certainly change behavior at runtime.  While I could disable the warning with a comment, ReSharper will always grey out the contents of the if block saying that the code is heuristically unreachable.