I can't say I discovered either item, just put the clues together. So if you are asking for undeniable proof, well I don;t have that, lust what I see as going on.
I will also add that in the "real world" I am a vacuum tech. Not a rug sucker but things like space simulation chambers and helium mass spectrometers and such, so I have a pretty good handle on vacuum theory.
So to your questions, the slide bounce is more common on US bikes (which might be due to the 45 pilots that come stock here) and was traced down with a mechanics stethoscope.
Why only the front does this at low RPMs IMHO is due to odd airflow from the short stack.
It actually make too good of a vacuum signal which causes the bouncing and also is what causes the stock set up to go rich on the front cylinder in the low-mids.
The fix, which is plugging one lift hole, was from HRC. They didn't say why, just stated to run their slide (with the single lift hole) with the short stack.
This causes the slide to react slower due to pumping through a smaller orifice. Which does 2 things first it stops the slide bouncing and also remove the rich spot from the front cyl.
Like all carb tuning, each bike will react differently but the rule of thumb is: With the long stock stack, run 2 lift holes. With the short stock stack, run 1 lift hole.
Aftermarket stacks (Dr. Honda) I have found work best for me with a lift hole plugged in each slide.
Loud pipes don't save lives, knowing how to ride your bike will save your life.