using 7.7.6 dashlet navigation does not behave correctly

as reported in GIThub https://github.com/salesagility/SuiteCRM/issues/2479

upgraded to 7.7.6 on dev and production instance and I also tested on new 7.7.6 install, all shows same behavior:
using SuiteR and Suite7 themes (the SuiteP theme seem to behave correctly).
in dashboad navigating to a dashlet works but behave incorrectly; the dashlet replace the dashboard, only the dashlet is showed in full width of the page