[support] Impossible to delete user picture

I am having an odd problem with user pictures. I uploaded one, let's call it Picture A. I then deleted it and my user pic disappeared. As expected. I then tried to upload another jpg image and got the message "the uploaded image was not an image". So then I tried another and Picture A appeared again. So I went to files/pictures and manually deleted it and ran through the previous two stages again with exactly the same results. One jpg got rejected as not being an image and magically, Picture A reappeared again. I am using simply Upload module and have never seen such malfunctioning with core modules. Has anyone seen anything similar before? Neil