Big, issue, you flip same coin 256 times, so you loose entropy
Care to explain that one?
If I flip heads 20 times in a row using a fair coin what is the odds that it will come up heads on the next flip?
Sure, there is no such thing as a fair coin, so throwing 256 unfair coins will be better than 256 time the same unfair coin

(50% for your question, whatever happens before, if the coin is fair (but it's not))