If you try to add an image with a '/' in the filename, Jira will try and alter the filename, and change the slash to a ':.'. This is considered an invalid character for an attachment, and so Jira will just hang forever and never attach the file. For SAC, or JAC, this is not the case, and you are met with an error message about the invalid character right away. See screenshot 1, for customer ondemand instance, and 2 for SAC.