i've posted a ticket already, but since there's tons of other tickets that lies there more than a year, i think the one that i posted will not be even looked at. so in case if somebody has the same problem, here's the description:
there's a line at top and left sides of a screen. it is one pixel wide and has #2E3128 colour. not very noticeable in bright areas, but annoyingly bright in dark undegrounds.
i have english nehrim and oblivion installed in different directories at d:\games, latest update, no mods, custom resolution of 1920x1200, and there is no lines at main menu or loading screens.
border exists on any save and in other resolution modes too, specifically in non-widescreen mode it stays between black stip and an image.
there is no such thing in Oblivion.