How to delete a keyboard shortcut I've inadvertently created?

So, I don't know what strange combination of keys I managed to inadvertently hit, but I have somehow managed to inadvertently give an existing Character Style a shortcut which is triggered by a single keystroke. And not just any key… 'e'!

So if I'was typing this very sentence into InDesign it would look like this:

So if I'was typing this vry sntnc into InDsign it would look like this:

Arghhh!

And yet if I open the Charater Style Options dialog the Shortcut field is empty.

Any ideas how to solve? (simply shutting down InDesign and reopening wasn't sufficient)