Explorer Scroll Bars Flash on for Fraction of Second & Disappear on First Open

This is the final unfixed symptom discussed in CORE-15429. Whenever Explorer is first opened the bottom scroll bars flash on for a fraction of a second and then disappear. The guilty revision for this being introduced is actually R75735 (Guilty Revision) by jimtabor and DarkShadow44. With the patch attached winpos_c.patch which reverts most of R75735, the flashing disappears, but the test programs referenced in CORE-3998 fail to show their ellipses. Maybe someone can find a solution that keeps the scroll bar from flashing on but still allows the ellipse programs to work. I have attached debug logs for the last good commit (R75734) and the guilty commit that caused the problem. Hopefully this will allow us to close CORE-15429. Note that I was not even able to detect the flash on my Intel Core i7 CPU running at 2.8 GHz using VMware Player 12.00.00. I had to create a test box on an older Pentium 4 running at 1.8 GHz running Virtual Box to detect the flashing, so the effect can be very subtle. Thanks.