One of my former colleagues(who wants to remain anonymous) notified me about this. Although many of you might not even be doing this, for just the few who are it is useful to know this caveat.
For security reasons some customers have the requirement to insert specific account information for every user. It appears that when you modify the details for “vpxuser” in /etc/passwd and the vpxuser password is refreshed these account details are overwritten. (Every 30 days the vpxuser password gets refreshed.) According to my former colleague this has been fixed in vCenter 4.0 but the “issue” does exist in vCenter 2.5 Update 6 today.