I noticed on the iOS version of Piwik Mobile, when you click on either “Visits by server time” or “Visits by local time,” it orders the hours by quantity rather than by time. On the full web version, these values are correctly ordered chronologically so you can see a progression from 1h to 24h.
It makes these two features very difficult to use, and it breaks the graphs. Only every third data point on the graphs are labeled, but when they are not ordered chronologically it is impossible to know the values of the two data points in between the labels. For example, my graph right now shows 19h with the most visitors, then ?, ?, then 15h, then ?, ?, then 20h.
Anyway, these seems like a pretty glaring problem and it ought to be fixed. Let me know if this needs clarification.