Broken rights on tmp directory

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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?

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?