While using the report/stats/index.php with "all activities" the gained statistics are different in the manner how moodle is displaying them: for 7months (and more) the monthly values are correctly lined up

and for 6months (and below)
the monthly rows are duplicated: one row of a month with the correct values and one extra row with just zeros as values.
Quiet similar to this here https://tracker.moodle.org/browse/MDL-36380
but with a single difference: the rows filled with zeros are occuring when chosing the displayed range of data under 7 months!

The graph is not displayed in a nice manner