You are right about VertRefresh (and about my having an LCD as my profile shows
Setting it to 60 Hz does resolve the black line question.
But... I still have a couple of questions:
1. Can I assume now that different values of NvAgp has nothing to do with the problem or solution and that that was all a red herring?
2. I'm still not sure why starting another video first also "solves" the problem, since this should not effect the refresh rate. What is going on?
3. Won't setting refresh to 60Hz (rather than the 75Hz max of my LCD) adversely affect fast moving action like games?
4. We still don't know what the root cause is of this problem and therefore don't know how to fix it or even whom to submit a bug report to, right???
Any other thoughts on next steps?