I don’t know if you ever got an answer to this one – over 9 months ago now I know, but I just found out that this can happen if you are on a MAC using Safari. It may be caused by Safari having the setting ‘Open Safe Files After Downloading’ enabled. So either try another browser or disable the auto-open setting.
Disabling the setting has just worked for me. I’d nearly torn all my hair out by that point though.
