See this LiveDoc, where it discusses copying bitmap data from one image to another, you can use several methods: clone(), copyPixels(), copyChannel(), and draw().As its name suggests, the clone() method lets you clone, or sample, bitmap data from one BitmapData object to another. When called, the method returns a new BitmapData object that is an exact clone of the original instance it was copied from.
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It's very difficult to understand what's wrong with your code without looking.
If you duplicate bitmapdata as in example all should be ok.
This is a common problem when you are passing instances of a displayobject like bitmaps to the source of mx:Image. If it is an instance, mx:Image simply reparents the instance so only the last renderer gets to actually display it. It is better to use classes or class factories so new instances get created. You can also use SuperImage from quietlyscheming.com to help you make copies of bitmaps
Flex SDK Developer
Adobe Systems Inc.