Hi Shawn.

It only happens when rendering at high resolutions, any high resolution at that. DPI settings makes no difference.

With regards to my tests with the Chrome and Mirror materials, it seems I was wrong and this did not solve the problem. All it did was shift the area where the Bucket leaves marks in the rendering. I didn't spot this until I started rendering the full image again later.

I've spent the entire day running test renders turning off / on options one by one until I found the little sucker that was causing the problem. This time I'm 100% sure I got this nailed down.

Can't tell you the exact name of the setting causing this right now as my laptop is rendering and will be for the next 8 hour. I'm on my Netbook right now.  I will post my findings tomorrow though.

All I can say right now is that it's a single option in the Atmosphere editor. I think it was on the Effects page, last option on the bottom right.

Regards
James