Chris,
When moving or panning around real documents you will often get these problems just because you are moving between fields with lines of text that can disappear between the fields.
The first thing I would try is to rescan the document at a very high resolution, 600DPI. This might get you enough information and make the text big enough to avoid this problem, though if you are going to zoom from full document to CU of one line you are going to have the same problems. Zooming from a paragraph to the line might work.
Another solution would be to make a decent size .pict and just let the editor do the move in Avid Marquee. I use AE and Adrenaline and for stuff like what you describe, marquee will handle it better.
Also, is it possible to not zoom? Why not show the document, full screen, then just dissolve to the line of text blown up. Or use the technique where you leave the full page doc up, it slowly gets darker, as a dissolve of the important line comes up over it.
Good Luck
johnny
Ck&Co