Sometimes with my Fujifilm GA645, when I shoot the final frame, the film advance starts and advances all the film onto the right spool. However, it does not shut off and keeps spinning endlessly until I open up the back. This only happens sporadically. What is the method the camera detects that all the film has been advanced and then shuts off. Can I fix this part of the camera so that it does not keep advancing endlessly? Thanks!