I have torn my hair this after dealing with a strange bug in Flex skinning.  When I created custom skins for the button, all of a sudden the skins would appear outside the boundry of the button.  In addition to the fringe, when buttons are rolled over, sometimes the skin is partially drawn.  I will detail this with screenshots later on.

Eventually, I went through and “break-apart” all of skin clips so that they don’t contain any references of common movie clip, the problem goes away.  The moral of the story I learn from it is that — “Try to limit the use of movieclips/graphics referenced elsewhere.”  Otherwise, the dimesions of the skin would be unpredictible.