CompuServe Messages

Folks, Probably painfully simple but…… When I detach faces from an object, ( a sphere for example ) and then reattach them they appear different when rendered. I was mapping an animated mouth to a block of faces on a toy plane. I applied Planar Coordinates and then reattached the section to the plane. when rendered it shows a seam. I thought it might be the smoothing groups but no such luck. Any suggestions as to what I'm missing ? allergy season has me a bit off my game… Brendan G.