portal: in case of diagram view back button (< or browser) should go back to actual previous view

In 10SR17 (and before) when the current page shows a diagram view and the user goes back to the page she/he is coming from, the view which is shown is not necessarily the one that she/he came from.
When the previous element is also a diagram AND the diagram view is configured, then the diagram view will be shown even if the user came from the overview or another factsheet.

Example:

For L1_process we have configured overview and diagram

For L2_process we have configured only diagram

When the user navigates from the overview page on an L1_process to an underlying L2_process and then clicks on the back button, the diagram view of the L1_process will be shown - which is NOT the page the user came from.

This is very confusing for NON analyst/designer users