Image display bug in flash 9?

hello all,
i’m having a strange image display problem where i load an external image onto the stage, then at runtime if i put a sprite over part of that image, say a pulldown menu covers the image temporarily, after the sprite goes away the image repaints with a 2 or 3 pixel offset from the uncovered part of the image.

this happens regardless of any dpi adjustment in the image or the image format (.jpg, .png, .gif). this happens regardless of whether i load from an external file or from the library.

any clues?

michael