If you look at the last scene of the sequence where they show Ginger being held captive in the coal bin, she is throwing a baseball against the walls. When they show her being thrown in, she had nothing but her clothes. When she is let out, the baseball disappears.
It doesn't matter what it is, it's a joke. The entire movie is a kind of parody of The Great Escape. They even use the same music. In The Great Escape, one of the men is always throwing a baseball against the wall when he's stuck in confinement. It's not a mistake, it's a tribute.