What I found most interesting is that Garmin's Mobile PC does not exhibit this behaviour. As I described in the original discussion, it behaves exactly as you would expect. Once you are zoomed to the level that starts showing the detail maps, the waterway details disappear and then begin to re-appear at the appropriate zoom levels as controlled by the "Map Details" setting.
I did not notice the equivalent of a "Map Details" setting in the other three programs (S&T, iGuidance, ON). That doesn't mean they aren't there, but if they are they aren't obvious to me.
...ken...