It was surprising to find no comment spam after installing WordPress 1.5, noting that I haven't enabled CAPTCHA with this upgrade. However I soon realized that I wasn't receiving any normal comments too on very commentable articles.

I realized yesterday the culprit was this option in WordPress: Blacklist comments from open and insecure proxies. under Discussion sub-section.

If you have it checked it prevents any comments whatsoever (even from myself) from appearing in the blog!

This is a serious bug in WordPress 1.5 release (Strayhorn).

Wordaround: Disable this option for now.