IE8 has some issues with @font-face when combined with :before. Bootstrap uses that combination with its Glyphicons. If a page is cached, and loaded without the mouse over the window (i.e. hit the refresh button or load something in an iframe) then the page gets rendered before the font loads. Hovering over the page (body) will show some of the icons and hovering over the remaining icons will show those as well. See issue #13863 for details.
But it does not seem to be this issue because we can NEVER see the glyphicon, in our case.