PDF widget zoom behavior

[David Epstein]

(LC 10.0.2, Mac) :  When I change the zoom of a widget (its pageDisplay is “single”), I would have expected its pageLocation to be unchanged if its pageGravity is set to center, and items 1 to 2 of its pageRect to be unchanged if its pageGravity is set to topLeft.  I don’t think this is what actually happens.
With pageGravity set to center, the pageLocation stays centered when I zoom to less than 100%, but shifts toward the lower right when I zoom over 100%.
Am I misunderstanding the system?  I am trying to keep the pdf centered as I zoom in or out.

David Epstein