How to eject/unmount stuck volumes?

Hello, a few month ago a minor issue appeared on my MacBook Pro 2012 with Retina display.

The problem is that, when a .dmg image is mounted can't be ejected/unmounted until rebook.

I've tried everything, force ejecting them, ejecting them from disk utility,

killing finder and do that again, deleting the "com.apple.finder.plist", log out and then log in again but nothing.

Only with a reboot the images are disappearing. Exactly the same thing is happening to USBs and CDs at the external CD driver!

When I force eject them, it says that the were ejected, but they are still on the side list in the finder.

I have searched the web the last months but with no results. It's not a very serious issue, but it has become very annoying.