GraphicsBitmapFill created by Flash IDE has invalid BitmapData

Hi,
I am trying to access a bitmap object which has no linkage and has been added directly to the timeline in the Flash IDE. When I look through the children of the display object container I see flash has converted all vector art and bitmaps in to Shape objects. The problem is when I use readGraphicsData to get a vector of IGraphicsData objects then the GraphicsBitmapFill object describing the bitmap has an invalid BitmapData object. Flash player will crash if i try and access it but the data is not invalid as Flash manages to display it fine on the timeline itself.

My aim is to compare which symbols are repeated in the timeline and ideally I dont want to go as far as comparing draw commands but I cant find any other way of getting back to the original symbol name given in flash which would be ideal. Comparing drawing commands works so far except I cant look inside the BitmapData object to see if the bitmaps are similar. Drawing each Shape to a bitmapdata object to compare them is not an option as there are thousands of bitmaps so it will take a long time to compare them all.

Thanks in advance,
Ross