Some domains running as www-data and being restricted from write permissions

Hi folks,

We've been running this box for 467 days now, it's got over 20 different domain names, 4gb of ram and generally cruises at around 2 gb.

It's a beauty, but recently, (either after one of my optimisation sessions or an update, or a combo of both), it's been misbehaving, where some domains that have wordpress installed have lost write permissions, I inspected and found that the chmod is still 755 and ownership stuff is still what it's supposed to be, I then looked at top (here's an example screencap 2 min after an apache restart: http://i.imgur.com/U2DTK.png , 3 min: http://i.imgur.com/sNPKs.png ), found that there's a lot more www-data users than there used to be.

So I did some googling and figured out that this could occur as a result of apache spawning a php process with www-data as a user instead of the relevant user it was supposed to be using.

I've gone through all configs and settings, all domains have "FCGId (run as virtual server owner)" selected, so I'm not sure why that's happening.

The only config setting that has www-data is the webmin/servers/apache/users and groups/ run as unix group-username, that has www-data selected instead of default, when I tried to set default, after a VERY long 'service apache2 restart', all sites timeout.

Disabling mod_php simply made apache force a download of the php files.

Can someone with a bit more knowledge than me point me in the right direction?

I don't want to chown all web facing directories to www-data, as that just sounds silly.

What can I do to ensure that apache runs php as the relevant user instead of www-data?