Are you sure the before commit MF is executed after pressing the save button? Is the MF not triggered after uploading the image? If I'm correct, the image uploader widget in Mendix will automatically commit the image object after uploading. This may be the cause of your problem...
You can always add a custom save button with a microflow which commits the object/image without events.
Jordy, thanks for your reply. Yes, the MF is executed twice after pressing the save button. See pictures. The second run, the object is already committed (state normal), so I don't know why that one is executed.