Unity regularly loses keyboard shortcut settings

My preference is to disable the keyboard shortcuts for workspace switching (ctrl-alt-arrows), as they interfere with some applications' shortcuts.

So in the control center I go and delete these shortcuts. Unfortunately, every now and again (sometimes after sleep, sometimes after reboot) Unity resets some of my keyboard shortcut preferences to the defaults.

I then have to delete the shortcuts all over again. I don't quite understand how the dconf key values could be lost so easily.

This happens in 14.04, and has been happening for at least a year of previous releases.