hello...
ahh - i am running ie7 via ie9 in compatibility mode, and that is not always true to the original...
i honestly wouldn't worry about it - here's usage shares for ie and then for specific versions:
http://www.w3schools.com/browsers/browsers_stats.asp
http://www.w3schools.com/browsers/browsers_explorer.asp
ie6 is actually over a decade old and ie7 is nearly that. both are primarily only still used internationally and in very strict corporate environments. if you have visitors with those browsers, they are likely used to seeing a lot wrong with most sites anyway as very few sites still support them any longer.
it is a css setting somewhere, but again - i'd let it go, myself as long as the site itself is functional...
sitruc