Each of my members has their sub-category where they can upload their pics, very straightforward. For now it's just me and my mods who are using the gallery till everything seems ok. So there are 4 sub-categories, one for each of us. I uploaded the first image and after that others uploaded a few others.
Now when I enter somebody else's sub-category and click on slideshow with the default settings, the first pic to be displayed is always that first one I uploaded (id=1). That happens in all sub-categories except mine, of course, where it "seems" to be ok since that first pic belongs in there anyway.