'fn' key shows desktop (not in combination with f11). How to turn this off?
iMac 21.5-inch, Late 2012
OS X Yosemite 10.10.2
Whenever I press the 'fn' key (standalone) key it shows my desktop, which it makes it difficult for me to use this key in combination with the f1-f12 keys. I had a similar issue on my Macbook Air, which was resolved by changing my keyboard to the correct input source and double checking that no shortcuts had been installed for the keyboard. When I realised that my iMac had the same problem I went through the same steps but nothing changed this time.
I've restored all shortcuts to default and made sure that my keyboard input source is one that matches my wireless keyboard.
Any ideas on how to stop the 'fn' standalone key from showing my desktop?
iMac, OS X Yosemite (10.10.2)