I'm able to reproduce the shift using these steps. It seems the Texture Each Tip box is the deciding factor if the behavior happens or not. With TET checked, I was not able to reproduce.
I also notice that on Mac (10.8.2), when you OK out of the Fade Brush tool dialog, the altered look gets saved to the pixels. Actually changes the brush stroke data.
But, when you OK out on Windows 7, the visual changes to the pixels shift back so there wasn't a change applied (unless you actually made some opacity changes or somesuch). The brush stroke data is not affected, although in the FBTool dialog the preview is definitely distorting with TET unchecked.
Thanks for writing out these steps, I'll log and have it investigated. Nice find guys.
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