Suddenly was changed the server user and write files with "apache" user and chmod 644

Hello,

Suddenly my server now write files using the "apache" user and chmod 644. Before, all the uploaded files when I create a node was with the ftp user and chmod 777. Just now, creating a node I notice that the image is not generated. I use the Watermark option of Imagecache Effects module, but just investigating the problem I discover that now all my uploaded files are create by the "apache" user.

I can't remember if really I change the password under Plesk to the FTP user and I don't know if this damage something in Drupal.