When the active page is switched, it's important
gtk_notebook_pages_allocate() is called after the bulk of
gtk_notebook_real_switch_page() is run, as the former allocates a
different space according to the currently active tab, which is set by
the latter.
gtk_notebook_pages_allocate() already calls gtk_notebook_redraw_tabs()
when the allocation changes, so just move its call down to
gtk_notebook_real_switch_page() to fix the bug.

https://bugzilla.gnome.org/show_bug.cgi?id=662629