The Problem
This is a known issue with Joomla. When you install any Joomla components thru Joomla's Admin section, all files are automatically upload & installed by Joomla. But the problem is, Joomla still keeps the file ownerships set to "nobody", instead of changing the ownership to your CPanel's username. "nobody" is actually a system-username which belongs to the Apache Webserver (that's the component which is used during the uploads). This issue is already documented on Joomla's site here.

The Solution
If you are hosted on a shared server, you will NOT be able to change the ownership yourself thru your FTP client or CPanel's File Manager. In that case, simply open a support ticket & let us know which files/folders needs to have ownership chnaged. Our support team will filx this for you easily.