Does Stopwatch.Gettimestamp ever roll over? Or roll back?

It's possible that you get the jump in time because your thread is jumping cores. See the "note" on this page: http://msdn.microsoft.com/en-us/library/ebf7z0sw.aspx

The behavior of the Stopwatch class will vary from system to system depending on hardware support.

See: http://msdn.microsoft.com/en-us/library/system.diagnostics.stopwatch.ishighresolution.aspx

Also, I believe the underlying equivalent win32 call (QueryPerformanceCounter) contains useful documentation: http://msdn.microsoft.com/en-us/library/windows/desktop/ms644904(v=vs.85).aspx