Users who use mainly custom date ranges in Piwik are used to seeing the sums for the whole period in tables and the days within the period in graphs. The image graphs (in scheduled reports) on the other hand behave like days/weeks/months/years in Piwik: The tables show the selected period and graphs show the past periods, e.g. for a week you see the week in the table and the last few weeks in graphs. We should offer both behaviors in the scheduled reports as well.
Ideally, there would be a switch when creating a scheduled report where the user can select the desired behavior. However, this is hard to achieve with the current architecture because the scheduled reports use the imageGraphEvolutionUrl metadata which is generated independently. The easiest way would be to add a config option that allows changing the behavior of evolution graphs (e.g., "General.graphs_show_evolution_within_selected_period" as there is already a setting "graphs_default_period_to_plot_when_period_range").
This ticket contains the quick fix and will be obsolete as soon as we have a porper implementation with a switch in the scheduled reports settings.
Also see the discussion about this in #3088. This feature is also related to #955.