I "think" you are referring to a Greyhole mount point? Of which there are no definitive answers as yet. I am aware the other Amahi users that use Greyhole are having similar challenges at the moment. I don't use Greyhole on my Amahi Production box.
We are using the current version of ownCloud (v4.5.5), "
http://www.amahi.org/apps/owncloud". If you are not at that release you will have to re-install the Amahi ownCloud package. Be careful, if you already have a lot of production data stored in ownCloud.
Also the "Samba" backend on ownCloud at the moment is "busted". I am not sure when the ownCloud Developers will get it fixed. I know for a fact that this V4.5.5 release of ownCloud fixed the mounting of local disk directories. I use that on my server. See Amahi Wiki page "
http://wiki.amahi.org/index.php/Media_S ... g_ownCloud", on how that is done in "Scenario 1".
You were indicating an ownership of "www-data"? You might want to also look at the permissions, the article above shows the ownCloud permissions requirements.