Graphics goes bonkers

[michaelbuffington]

On a MacBook Pro (Retina, 15-inch, Mid 2015) running OSX 10.10.4.

On this particular design whenever I try to create a new sketch or edit an existing sketch the rendering basically loses its marbles (see the attachment).

I've also included screenshots of relevant settings.

[michaelbuffington]

I should have also mentioned - the issue resolves itself if sketching is stopped.