This is needed because of the shadow implementation (EnableShadow=true). When a RadWindow is set with that property, it uses the PNG image in order to provide semi-transparent, rounded shadows. When that window however, is set inactive (e.g. when you click on another window opened on the same page), it starts using the GIF file instead as the transparency is not needed at this point. This is happening only if EnableShadow is set to true. If it is set to false, only the GIF is downloaded.
As for the icon image, it is placed in the sprite for convenience. Even if we remove it from the sprite, its size will not be significantly reduced.
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