exactly the same happens to me. the viewport seems to ‘forget’ what to draw, or maybe draws more than 1 view at the same time over the active viewport. this could maybe answer the flickering…
one difference to your problem: in my case the ‘split viewport’ doesn’t change anything.
http://discourse.mcneel.com/t/amd-radeon-hd-8670m-open-gl-issue/4775/5