I recently noticed that the question/answer-level summary of reputation changes that you get when clicking the daily reputation bars doesn't match the correct day. Instead you get a list of the reputation changes during the previous day.
This screenshot makes this clear, and the list shown below belongs to the day to the left of the grey bar:
also, where the list is empty since it is showing reputation changes for Jun 6, and not the selected day:
I noticed this at BiologySE, but have the same problem on StackOverflow. I'm using Firefox 38.0.5 on windows 7, if this should make a difference.