Aperture 2 export problem, shadows/highlights

Using Aperture 2, I exported the wave shot I posted in the last entry, and it came out a large blemish / artifact in the sunball. After some more testing, I discovered that it was an effect of the Shadows adjustment.

image taken from screenshot of Aperture 2

Here are the settings I used:

image from Aperture 2 export with Highlights at 0 and Shadows at 0.8

In the image above, look for the large horizontal line in the sunball. It's actually a large checkerboard pattern, with a second dark rectangular area just to the lower-right of the obvious one.

Here's a close-up of the bad area:

With Highlights & Shadows disabled, it looks fine:

Image was taken with Canon 1Ds Mark III, and processed in Aperture Trial 2.0 3A86.

Full adjustments made to the image here: