If you select any other metrics than "Visits" in "Visits per server time" "Vertical bar graph" is sorted on values (from low to high). This is wrong since you lose "time envelope" . It should be sorted along X axis -> time.
Same error with sorting is also present in "Visits per local time" and maybe some where else where X axis is hour scale.
Best way would be to have configuration option with icon "plugins/Zeitgeist/images/configure.png" and we can choose along which axes to sort.
In c1418485c492a3fb6952955e7c746ea54cf55049: fixes #4541 sort column changes when selecting another metric in VisitTime