I believe the last two updates to Domain Mapping may have introduced a bug that can cause a redirect loop for SSL-protected pages. The following page presents the issue: http://advpools.net/payments/
What appears to be happening is this:
1. The visitor hits http://advpools.net/payments/
2. The server enforces a backend redirect which forces pages ending in ^/payments to https://
3. Domain Mapping (or some other plugin) rewrites https:// back to http://, resulting in a loop.
This site was functioning as expected until the last week or two (perhaps a little longer), when the redirect loop suddenly appeared. There have been no other changes made to this site other than plugin updates.