Snow Leopard TextEdit's Command-S

I've just noticed that the keyboard shortcut Command-S no longer saves a TextEdit document on my MacBook. I get a rude 'thunk' error sound instead. All the other Command- shortcuts work fine, e.g. Command-C, Command-X, even Command-Shift-S for 'save as'.

I running Textedit 1.6 on a MBP 10.6.8. I don't have MS Word or Excel or any other application installed that I could experiment with.

Anyone experiece this?

Greg