I only submitted a black background during the "Open" phase of the contest. The other designers submitted those during the "Open" phase as well. During the Open phase anyone is able to submit anything at anytime. Your contest has now moved to "Top Five" which only the top five ranked designs can upload new artwork, but since no one is ranked, designers can no longer upload new artwork or make changes.
Hope I'm making sense. Let me know if you have any questions.