I would like to submit this issue: When quotas are configured in "Total server quota": (take the total space used by : mail + ftp + db) the quotas returned in the system info page (home page) is correct. But, if you configured with "Server administrator's quota" (only take "web space" = ftp + db and no mail) the quotas returned in the system info page (home page) is not correct at all.
if fact, each quotas (the right value in the charts) returned in the sytem info is the GROUP quota in state of the USER quota ! So the graph is wrong.
Also, if I go to the user quotas (via system/disk quota), and I have a look on a specified quota (defined in Server administro's quota), all is fine : the total quota and the usage quota, for each users.
More complete details submitted to "authentic theme" (because firstly I was thinking is a "theme" problem) : https://github.com/qooob/authentic-theme/issues/195#issuecomment-117020219