Can't "uncheck" items in sort-by

[nsepe]

Hi there. For some reason the admin isn;t allowing me to uncheck the sort-by boxes. See screenshot of what won't go away. I un-check, save, and there it is again! Any ideas??? Thanks!

[nsepe]

Here is my screenshot, forgot to add...

[attachment cleanup by admin]

[jenkinhill]

You must always have at least one sort-by selected - this is necessary for the product display.