This is a bug report for the developers amongst us. In 6.7.1 (should be the current version I believe), on my system anyways, I've encountered the following behavior with buttons/labels and bitmaps:
If I create a button/label with the -bitmap option in the named options/hash, then the graphics work properly. If I wait, and use the SetImage method after creation, the button/label doesn't show the bitmap. Regards, Greg