[overlordalex]

This is actually due to a psychological thing where humans don't find long strings of repeated letters/digits "random" and hence will flip more frequently than you'd expect from a machine.

I also recall there being a problem in the use of 5-grams which lead to a sequence in which it guessed 0%, but I'm struggling to find it now.

[js8]

If you would find the sequence I describe in my other comment, I think you would almost get that result, because you would (except at the beginning of the sequence) always pick the k-gram that has been seen one time less.