The url path for a user profile only shows the name for members who belong to a usergroup with Public as a parent (except for registered) but it shows userid-username for members who belong to a usergroup with Registered as a parent and/or they belong to Registered.
There may be another logical explanation but I assume the profile path should always finish with just the name only?
I have tried directly logging in to the profile as the user, going via the friends link to profile as well as from the leaderboard module.