Comment 29 for bug 546338

I'm affected too. See http://launchpadlibrarian.net/40660364/Screenshot.png for another screenshot.

If any devs want to try to reproduce this problem, please make sure there are conversation lines *before* one with a newline in it, since there's additional weirdness going on depending on whether the offending message opens a conversation, and whether there is a chat history to display or not.

Also, note that the missing lines do display in the chat logs, even though these use the Ubuntu theme too. It's the real-time window updates that fail.