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...
What he's saying is that it went from april 29th to may 30th, when it should have gone from april 29th to april 30th.