Comment by robinhouston

Interesting! I did a maze flooder last year http://bl.ocks.org/robinhouston/6023888/653206574a69127d7fa2... using uniformly random mazes[★], and the flood-filling is much less uniform. The uniformity here must be a reflection of the way the maze was generated.

★ There are algorithms that generate each possible maze with equal probability, if by maze you mean a spanning tree of the grid graph. I used such an algorithm, Wilson's algorithm.