Thanks again to all.
@oldjim: The location of the config files was changed some time ago in response to user requests. Because there wasn't universal agreement I included the option to choose one of two locations, both of which should be accessible to the user. I think I'm going to leave it that way.
@NewtronStar: I think your second experience may be a red herring. If an MDWS upload is delayed for any reason, such as a temporary network issue, the GUI freezes and doesn't redraw until the temporary blockage clears. I think it's most likely that this is what happened to you on that occasion.
@tbailey2: The occasional divide by zero error has been bugging me for a long time, as I've never been able to reproduce it and haven't been able to locate a cause. The best suggestion so far seems to be to set the error averages to the 24 hour setting, not the modem uptime setting, and this seems to have fixed (or at least alleviated) the issue.