I just had the need to correct someone's photo in Family Tree Builder and the website. If you just delete them from the associated people list without unchecking the personal photo checkbox, the photo remains on the family tree diagram and you can't remove it. The workaround is to associate another photo, make it a personal photo, save it, then uncheck the personal photo then disassociate the person. Surely this is a bug. It should work by simply removing the person from the association list.
