Really wierd "File system" not writable problem...

Installed aegir a couple of days ago - and I really, really like what it offers!

But I have a really wierd problem with the "File system" settings...
It says:

• The directory sites/[testsite]/files is not writable
• The directory sites/[testsite]/files/tmp is not writable

And I have "even" tried chmod 777 on the folders!!!

The main hostmaster aegir site works and validates that the files folder is writeable - and if I chmod that to 550 it complains... why can't the hosted sites connect to their files folder??? What am I missing and how can I solve it?
This is so both on imported sites and on aegir created sites - both on my own created platform and sites made on the "hostmaster" platform.

The imported site also works - ie. the paths aegir sets up to the files folder is the right one - but somehow they are write protected... and I am ripping my hair out because by now I feel like I have tried EVERYTHING :( here Goes:

chown the files directory to aegir:aegir and www-data:www-data - the default: "aegir:www-data" is what the hostmaster has and what seems to be the right...
chmod the files directory - even to 777 - no luck...
Override the settings.php to make it possible to put in another/my own specified directory - no go... tried to use other folders now write protected, create new ones etc. The only thing I got "working" was to use /tmp :/ - but I can't see any difference between /tmp and my files folder... (except that the /tmp folder has sticky bit set - "t" or chmod 1777, which I tried to no avail as well)

So I feel like there is some sort of thing hidden from me - and it led me to look into some SELinux stuff and an ls -lZ reveals only "?" as all files and folders contexts ALSO the /tmp folder that worked :/

Please can someone point me in the right direction...