Original thread: http://forums.adobe.com/thread/856834?tstart=0
I have now tracked down the cause of the flashes and they are definitely caused by using the Nik software directly from Lightroom.
If I send a dng image to Photoshop using LR external edit, modify the image in Photoshop using the Nik plugin(s), and then return it to LR by saving it in Photoshop everything is OK.
If I send the photo to Nik directly from Lightroom then the flashes and other problems appear. It is apparently tied to images sent through the Nik software directly from LR. I can manipulate any image not sent to the Nik software from LR without difficulty. Returning the the image sent to and returned from Nik again causes the flashes.
The annoying flashes happen quite often in the develop mode when working on an image edited directly in Nik software from LR. This makes the develop module virtually unusable after sending an image to a Nik plug-in.
I've placed a video clip showing the bug:
http://gpsinformation.org/ronh/images/Lightroom - Nik bug.m4v
I will be reporting this to Nik.
The video file will be removed from the web page on or after June 4, 2011.