I've played a litte with the "DashboardBackend###0130-TicketOpen" widget.
I essentially added this "SortBy=Priority;OrderBy=up;" in the "Sort" attribute.
I applied and deployed my modifications.
When I refresh the dashboard for my user, no luck.
My tickets are not sorted.
I went in my dashboard config (upper right panel), un-checked the widget and saved.
I went back in there "checked" the widget and saved.
So change, my tickets are still not sorted.
I must have missed something really obvious but I seems I can't figure it out.
Thanks a lot for your help.