Ah, rprentki - I talked to good42n in chat about this yesterday. Forgot to put an answer here as well.
The "problem" was, that there are two grey pieces visible in the overview (The long one at the bottom and the small one in the upper corner) and if either both parts should be colored (even tough they are not connected directly) or only the AI one.
Delayed answer: Only complete the path the AI started for you. This has something to do with the hierarchy of those cubes. Especially in the Starburst Challenge it is possible that two branches are visible in the overview in one cube - but belong to different cells! Coloring both would confuse the AI and enrage the GrimReaper :)