spaces switching unexpectedly on osx yosemite I'm having an issue where my spaces keep randomly switching without me doing anything.

I haven't managed to work out any sort of consistency to the behaviour yet so impossible to reproduce, but I'm trying to find out if anyone's had the same problem and knows how to fix it?

I'm running OSX 10.10.1 on a Late 2008 aluminium MacBook.
System Preferences > Mission Control > uncheck Automatically rearrange Spaces based on most recent use