I'm migrating a large number of stand-alone pages into content pages. Most of this involves little more than copying and pasting a GridView from one page into the new page. However, I find that styling disappears in the new project, i.e. the styles (as classes) are still present in the stylesheet, but these classes are no longer applied to GridView table elements.

Example, in the old project, once a table is rendered by the GridView, its header row has a class of HeaderStyle, but in the new project this is lost, without any editing of the GridView. Is there some mysterious, built-in mechanism that automatically applies these attributes to GridView elements that I have somehow disabled?