Anchored Frame constraint on opening xml file

I'm using the DITA application provided with FM8 on WinXP. A curious situation arises with graphics (gifs) that are read into an anchored from, particularly when the graphic is large; the width is being constrained to 612pt, which is distorting the image, and then affects (narrows) the specified width of the image in the xml.

Where is that constraint coming from, and how can I remove it? It's not represented in the xml source, and I'm not seeing a setting in FM.

Thanks for any help
Bruce