This is by design. It's not a bug, and it's always been this way. The reason is that once you have created your account, too many programs hardcode the user path. If you change the folder name, all of those programs will break. The fault lies squarely with the developers of those programs, but guess who will end up getting the blame if they crash? Microsoft. It's completely unfair, but it's how it is - Microsoft get the blame for application crashes completely outside of their control.
So they thought very carefully about the two options and decided that keeping all programs operating correctly was the number one priority (not so much as a way of avoiding blame and hate, but because they want everyone's computer to run smoothly, and making sure that the computer runs as well after an account rename as before is very important to them). So they decided not to rename those folders but leave them with the old name - ensuring that all apps continue to work.
If you wish to run the gauntlet, you can attempt a manual rename of that folder. Any apps which break are likely to need reinstalling - but they should work after reinstalling as then they see the new user folder path. The article I'm about to link to is for Windows 7 Professional, so you're going to need to ignore the screenshots slightly and use alternative methods at the Group Policy Editor bits, but it really shouldn't be too difficult to see what to do since mostly those bits are just "rename the user account", or "create a new user account".
How to Rename a Windows 7 User Account and Related Profile Folder - TechNet Articles - United States (English) - TechNet Wiki
Alternatively, a slightly safer method is to create a new account under the new name (rename back the old one first), and then copy all of your files/emails across. Then all apps have to re-run the user account specific setup and that resolves the problem too.
There are actually extremely few bugs in the "normal" bits of Windows, and those bugs/deliberate hacks which do exist are almost always caused by 3rd party programs not following the rules.
Richard
