Some files created through Joomla's admincp will automatically give it 755 and sometimes 777 perms. Joomla also chowns the files and directories it creates when installing modules and components, making it almost impossible to edit and add files via ftp client.
Shuttle XPC | Intel 865g | P4 3.2Ghz | ATI 9800 Pro
Hosts: Ubuntu 6.10 ~ XGL-Beryl SVN-Gnome | OS X 10.4.8 | WindowsXP
Virtual Appliances: Ubuntu Server 6.10 | WindowsXP | CentOS 4.4