Bug in Nik Silver Efex Pro 2 on Windows or with Lightroom 4.1?

Just set up a new workstation with Windows 7 and the latest versions of Lightroom 4.1 and Silver Efex Pro 2. When I "Edit Photo in Silver Efex Pro 2" and choose a 16 bit TIFF as the export, I get these lines or bands in the image (see example attached to post). It seems particularly related to structure adjustments. This does not happen if I use 8 bit TIFFs, it functions normally. (I'm using sRGB color space and no compression.)

Also interesting is that I can see lines while processing the image, but when I save it back to Lightroom, the lines are in different places...

Has anyone else seen this? +Nik Software? Any ideas?
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