The menu flush placement is a side effect of a philosophy change in menu display options.
If you have Weaver Xtreme Plus, you can add wvrx-fullwidth to the add class box on the Primary/Secondary settings. The will return to the way Extend BG menus looked before with the bg color going full width, but the menu left aligned with the theme width.
Weaver V5.0.4 will add the ability to add a class (wvrx-fullwidth) to the primary or secondary menu without the need for Plus. Should be released in a few days after some more time for other possible issues.