Following Rodney's step from the escalator on the red pedestal he is being scooped into one half of a wire-frame globe/ball. Two halves now (the other one has Fender in it) form an intact globe. A safety bar with a 'wooden' middle bit (like those on rollercoasters) suddenly appears. After their journey, when the ball splits back into two halves, the safety bar, which previously had mysteriously appeared, now has disappeared.
Not a mistake as such, but interesting to note. When Rodney and Fender are in Fender's room, lying in the hammocks, look behind Fender on the wall. Behind him is a "robot" version of the 'American Gothic' painting from the Rocky Horror Picture Show.