Interface Details and changing resources

On my Interface Details view, I have the built-in "Min/Max/Average bits per second - Today" resource at the top of the right hand column.  However, it keeps modifying itself to use "Last 12 Months" as it's time frame.  I remove the resource, re-add it, and it's fine for a little while, then eventually it goes back to a 12 month view.  Any guesses on what's happening?