On my blog, LonePlacebo.com, replying to a comment redirects me to a page that looks like http://loneplacebo.com/readable-making-the-web-easier-to-read/comment-page-1/#comment-14092. The page shows a 404 message as well. Shouldn't I return to the original blog post?
Something weird is going on. I just tried to leave a comment and it wouldn't accept my url. It said it was invalid, but I can't imagine why?
Then I when i submitted the comment, it took me to the page not found as you mentioned, yet the comment shows up...
If no changes were made the templates recently, I would deactivate all plugins and see if one of them is responsible.
What browser are you using? You may want to look at it on Firefox. The facebook like button is misaligned.
Well, I've found a partial solution from this forum post: http://wordpress.org/support/topic/erroneous-comment-page-1-in-comment-url-generated-after-commenting?replies=9
I disabled comment pagination. Not exactly an ideal solution, but it's better than 404's.
Regarding the Facebook buttons on Firefox, I have no clue. This doesn't seem to be the case on Chrome, Safari.