I will ask again, am I the only one seeing this:
Date: 30.5.2013: Reward 425.26716892714285 BTC
Date: 30.5.2013: Reward 506.74909089 BTC
at mining.bitcoin.cz graphs
I assume you are wondering why there are two values for a given day - even though you don't make that clear at all...
You are looking at two functions plotted on same graph - a 7 day moving average and the actual data point for the day...