Hi there, thanks for the update! I've determined that it's in MediaWikiChat.js and the problem should be on line 312 - this is currently the line that calculates the value for the rowspan attribute. I'm going to talk with some other MediaWiki developers who are also familiar with JS so that hopefully this bug can be solved faster.
oh and the circle icon you saw - "it's not a bug, it's a feature!" really. :P It shows up to indicate that your messages are currently in the process of sending whenever you submit a message.