Reset Screen Resolution - Bad Result

My GNOME2-2.24 setup works well at the default resolution of my monitor (1280x1024). Applications display well. If I reset my screen resolution (using System->Preferences->Screen Resolution), it restarts okay, but then, and upon every subsequent reboot, many of the application windows open using only half of the desktop real estate. For example, firefox3, thunderbird, openoffice, all of which would open a main window using all of the screen, now only open using half of the screen (half-length). If I reset the resolution to 1280x1024, windows open full-size; if I reset to 1024x768, windows *now* open full-size; if I reboot, windows open only half-size again. Has anyone else seen this? BTW this is about the fifty'th time I've installed GNOME from ports or packages; I've never seen this before.

Note that I can unset from full-screen (so to speak) and drag borders, but I have to do this every time I re-start the app, even in the current session.