Hi everybody,
The EX codec was implemented by the FCP update 6.0.2 or higher versions, and you can check if the file is installed correctly by looking for this file in the following folder:
/Library/Quicktime/AppleHDVCodec.component
The file must be about 1.6MB, otherwise is an outdated version.
You can see the clips in the Clip Browser because there you only see the proxy clips, not the high resolution ones.
Don't forget to use the last Quicktime version available.
In the camera, the mode doesn't matter, it works in both camera or media mode, when you plug the USB the cam prompts you confirming the connection.
Hope that can help