The menu becomes bigger vertically, and the left and right side components (Page title on left, the button that opens the jQuery-menu on the right) are partly outside of the site.
See the screenshot and try to scale the browser for yourself.
I have the same issue, have you found a solution ?
This is caused by the extra margin added by class: .navbar-relative-top, in bootstrapwp.css in line 6193, which by the way is no longer present in the latest versions of bootstrap.
@media (max-width: 979px)
margin-left: -20px; <===== here
margin-right: -20px; <===== and here
If you change the navbar class from navbar-relative-top to navbar-fixed-top it should work as expected.