Broken rights on tmp directory

Server
1

Continue from https://central.owncloud.org/t/error-uploading-file-filename-error-write-on-disk/1828

The right to change when i restart the computer on directory /var/www/owncloud/data/tmp....

I need to run chown -R www-data:www-data /var/www/owncloud/data/tmp every times after reboot.

How fix this?

2

Is this a special partition or just a folder? Normally the permissions don't change itself, there is probably a process related to it. Can you give more details?