There are similar issues to this raised before, and in general many about multiple monitors since Unity, but not this precise one, and no complete answers. I have a couple of Dell Precision laptops (most recently M4600 - with nvidia quadro 2000M gpu), which have Fn+F8 as the dynamic display switch (loops round laptop -> laptop+external -> external only, like most laptops). Until Ubuntu 11.04 this worked fine (for several years) but since 11.04 its been broken. Just doesn't work. I've tried to find solutions, hacks, etc, have posted on official ubuntu forums, but it's just broken. I travel a lot and give a lot of (scientific) presentations, and really need this functionality. Since 11.04 I have to stand up at a conference, plug in my laptop and then go through the hassle of nvidia-settings, detect displays, mirror displays, apply, etc. Argh. Its the biggest issue I've had with Ubuntu in years. I've taken to giving other people PDF files to show on their laptops, which excludes me from showing animations of data, etc. Here's hoping I'm being daft and someone can help me out. Note that the projectors used are all different in different places, so they have to be dynamically detected each time (but, then again, 10.10 and all previous Ubuntus did this fine.).
You could try the Disper utility and the Disper-indicator. It won't (yet?) work with the keyboard shortcuts. Instead it gives you an indicator icon from which you can choose the desired monitor setup.
The Disper utility works with both the XRandr backend and the proprietary NVidia driver (though I have only tried it with the nvidia driver).
Check it out:
Disper ppa: https://launchpad.net/~disper-dev/+archive/ppa
Disper-indicator ppa: https://launchpad.net/~nmellegard/+archive/disper-indicator-ppa
All the best N