See for example page 
When a user selects a 3 month period, that choice will be preserved when the user clicks from e.g. 'overall total' to 'per page type'.
But not when the user switches from 'editors' to 'edits'. Then the reporting period resets to default 'two years'.
I expect users will want to compare different metrics using settings unchanged.
This allows A/B comparisons by quick alternating between metrics, having an intermediate chart with unwanted period, makes that a bit more tedious, but also erases short-term visual memory.