Photoshop :: Black Square In CS6 When Using Nik HDR Efex Pro 2?

I just got Nik's HRD Efex Pro2 and I'm having trouble with it. System is iMac running OSX 10.8.3 with 12Gb RAM. When I come back to PS CS6 from HDR Efex using either a Fuji X-E1 or Nikon D800 RAW file, the effect is properly rendered but there is a big black (or sometimes white) box somewhere on the image. Once this happens, all subsequent images loaded have the same or similar defects and the only way to get rid of it is to shut down PS and restart.

When I save the file despite the apparent defect and then look at it in LR4, the saved image is fine so it appears to have something to do with how PS is rendering the image on screen. I called Nik and they said it was a memory problem (a leak) in PS CS 5 and 6. I suppose that is predictable. Nik suggested reducing the size of the available RAM (I'm now at 56% down from 69% which is in the "ideal" range) and changing my Drawing Mode from "advanced" to "basic". Didn't work.