There is supposed to be an option to give yourself a display name that appears whenever you post. Your account name has no spaces and must be in lower case. The display name will allow you to have upper case characters and spaces. That appears to be one of the bugs they're having right now, but it's on their list of things to fix.
I was one of the people testing the new board, so I had set up my registration when the display name field was partially working. However, it had a bug that caused it to break if you changed some other setting, so I was all lower case too last time I was on. Then when I logged in tonight.. tada! I had an upper case M. I don't know what happened.
I do know that it's just a bug and they'll probably get it fixed soon.
I had a capital N for Nightingale but then I registered and logged in and the capital disappeared. Oh well. As you say, just a little bug. But I'm OCD about details like that in language so I seriously need for them to squash that bug and give me back my caps! :)