Steps to reproduce the issue

Move your files folder outside of your joomla root and put a symlink to it in its place. A totally normal thing you might want to do.

Expected result

Since this is a totally normal thing and it has always worked until now, you'd expect it to work exactly the same as if your actual files folder was there. In other words, no different from a completely standard installation.

Actual result

You will not be able to navigate past the base files folder (COM_MEDIA_BASE) because of this great little addition on line 116 of the media manager's list model:

// Reset base path
if (strpos(realpath($basePath), JPath::clean(COM_MEDIA_BASE)) !== 0)
{
	$basePath = COM_MEDIA_BASE;
}

System information (as much as possible)

Some kind of linux.

Additional comments

Change it back.