That's fair I guess. My vision must've blurred because it was during the launch sequence. But I really positively thought I saw a disconnected Rivals train in there... Maybe it was a dismantled Superman train. I didn't see any other colour except for black seats and grey as well as steel checker plates there.
I remember during the most recent school holidays, one of the staff members told me (when Rivals was open and only operating one train during three-hour waits) that the second train wasn't in the Rivals maintenance bay, but in fact, somewhere else within Movieworld - that's probably what lead me to think the above statement.
Does the little maintenance bay/s within the Superman footprint (next to the launch track) get utilised by other attractions? I remember seeing a few Green Lantern carriages there during the Christmas holidays...