Hello Tom, it is the intended behaviour of the operating system. Try to plug in a USB stick , then open terminal and cd into it, and then try to eject the USB stick. You will get an error that the stick cannot be ejected.
This is to prevent removing the media if there is an open file on it. If you would force removal, there is a good chance that the document open would be damaged.
Same is with espionage, we cannot eject he disk image as the OS X does not allow us. We might force it, but we do not want to, for the aforementioned reason.
I'm not sure about Espionage 2, but at this point it does not even matter, as the current behaviour is the correct one.
Rgds
Zsolt