Even with the latest public build, users frequently report that they only see one name in the user list, a bug that has been impossible to reproduce for me. I initially suspected a network problem, but everything else (A/V stream, text chat) appears to be unaffected. The user list is written correctly to the writeuserslist.php script, so it is most likely only a display issue.
But maybe there is an illegal character in the name of a user who is logged in at that time that causes the rendering of the user list to fail. Being a German language site, usernames may contain special characters such as ö, ä, ü and ß and also all kinds of punctuation characters and spaces.
Could it be that one of these causes the display of the complete userlist to fail?