You need to have a minimum of 8 images before uploading, otherwise they will just keep being expunged. Also make sure you don't try to break the limit on how often you are allowed to update, twice per 30 days is the limit.
It is also probably not a good idea to update simply by switching a couple of the images around as you did here as that makes it appear that you are simply bumping your gallery to get it back to the top of the results. You could get banned from uploading at all if you do that.
I'm not trying to complain or get anyone in trouble, but could someone message me on the forums the rules of updating galleries, specifically if you are the artist of the gallery subject matter? I'll get back to whoever does on why I'd like to know.