This bug still exists in 6.31. I've seen this exact issue in my custom windows quite a few times, but thought I was missing some switch for /window that would fix this and that I hadn't discovered yet. Never considered it to be a bug...
So after reading this, I tested it with the example the OP provided right away, on a clean 6.31 install, and just as expected, part of the message didn't show up. As the OP said, the text after the tab char is always displayed; the amount of text before the tab not being displayed varies depending on the font being used.
Not sure how some people can not be able to reproduce this though, unless other factors like OS play a role here.
Tested on Win XP Pro SP2
