This appears to be a race condition: We are saving the Report/Dashboard and switching to view mode. This switch to view mode causes a re-instantiation of the Report/Dashboard component, loading the content. Depending on whether or not the backend already processed the saving, we get new or old content.
Previously, a route change did not trigger a re-instantiation of the Report/Dashboard component, so that we did not need to query for the Report data from the backend. As we changed the way the Router resolves paths to components in OPT-1018, this bug was introduced.
Same behavior appears to apply for Dashboards, too. Very strange.