A person with a similar problem has found a solution at this link www.computing.net - ie7-default-paper-size.
He/She found that IE would revert to 5.08mm bottom print margin if an attempt was made for anything below this measument. Your 4.09 may be kicking this very trigger and thus IE reverts to it comfortable 5.08 when you switch printers.
IE would not set the bottom print margin to anything less that 5.08mm via the page setup menu, it would automatically revert to this number if something smaller was entered. Changing the margins in the registry (hkey_users\\Software\Microsoft\Internet Explorer\PageSetup\margin_bottom) stuck for smaller margins.