Thanks to all for the tips on Scrolling / highlighting in NoteTab.
I'm satisfied I guess, to know that the problem is universal and not confined to my configuration.
I made a discovery of sorts today - the excessive scrolling rate is much less grave, if I keep the cursor away from the left margin. I can move it back there if I must, when I have ended the scrolling.
If this has always been common knowledge, Jody will undoubtedly be pleased if no more than one or two of you tell me so.
Thanks for all the hints.