I've noticed that a lot of issues with banned proxies and e-mails have to do with posting to forums, specifically...
The only field I left as default was Forum Subject. Maybe that's the issue?
What other fields in the project data panel are used to create a forum post?
What about the Forum Comment? Is that used with the Forum Subject?
Checking, seems I must have disabled [ ] Forum Post as type of link to create (in at least the projects I've checked so far), so I guess I had just disabled this some time ago because of the reports of forum sppam.