I have noticed that many times when zooming in or out of the map (using either the scroll wheel or pan/zoom bar), the base overlays are not redrawn. The custom overlays I have on top of the base overlays are redrawn (and zoomed accordingly), but the base overlays are not redrawn. I should add that I am sometimes hiding and showing different base layers based upon user interaction with other page elements, via getLayer(overlayName).setVisibility(false/true), just in case that fact is related.
What would cause the base overlays to not be redrawn, and is there a method for forcing them to be redrawn?