You can jump from the bonus level to the previous level in the map GLXY.
Here is proof for the Tower Unite team: https://www.youtube.com/watch?v=RqsJQYispHU&feature=youtu.be (not that you need it)
Heh not a bug its a feature 
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Please explain.
Ball race is known for having many secrets and shortcuts. Whether this one is intentional or not I don’t know, but it wouldn’t surprise me if it was intentional