hello. any of you know what is going on here? as soon as i start extruding or merging verts or edges or anything, parts of my mesh lose all of their surface info and revert to simple wireframes. i can still apply textures after the fact, but it keeps doing this over and over, and i'm afraid it will cause problems when i export as an obj later.

some relevant info: maya 2010 on macbook pro; i have already ran the cleanup tool (n-gons, faces with holes, nonplanar faces, lamina faces, nonmanifold geometry, normals and geometry, and edges w/ 0 length checked) multiple times, but it keeps doing this regardless.