I am very sorry for the delay in getting back to you. I have been rather swamped the past few weeks.
With the additional information you provided I was able to see almost exactly what you described, though I have been experiencing a series of (hopefully) unrelated crashes when trying to reproduce this issue in our latest internal build of the Engine. I am in the process of reverting to a slightly older build to see if I can avoid those crashes and complete the test in our internal build.