Randomize not working..

I have banners on my site in size 300x600px. Despite specifying them to all be in the same group, when new banners are added they are vertically added to the bottom of the previously added banner. Ultimately creating a page so long, it takes forever to scroll down it. Strangely enough, with all the same settings, my 300x250px banners are rotated each time the page is refreshed rather than vertically stacked on top of each other. Can anyone tell me why the heck this keeps happening. I have clicked and switched on and off everything I possibly could in hopes for a change, but still only get a string of banners vertically stacked on top of each other, creating the world’s longest internet page. PLEASE HELP!

http://wordpress.org/plugins/wp-bannerize/