Dictionary.com listed 'Canceled' as the past tense of Cancel, where 'Cancelled' as a British spelling of that tense.  http://dictionary.reference.com/browse/canceled

Merriam-Webster merely lists both forms as inflected forms.  http://www.m-w.com/dictionary/canceled

I'd love to understand why "Log" goes from in/out to on/off and "Sign" does the opposite and goes from on/off to in/out.

There must be a deeper meaning here...  Is there an important semantic difference between Log[in|on] and Sign[in|on] that warrants different naming styles?

Sorry, just being picky and I wanted to try out the community content feature!

If you'd like to override the preferred terms and use British English for 'Cancelled' rather than the American version 'Canceled', forget about it. Even if you put it in the the CustomDictionary.xml it will be overridden by the built-in rule.

  <Deprecated>
            <Term PreferredAlternate="Cancelled">Canceled</Term>
  </Deprecated>

... because it's English English, not American English - and the American's fired the English as the arbiters of the language a few hundred years ago. *grin*

ps - I'm 50% English and 50% American, grew up 'over there' but now live 'over here' (and does it matter which is which?). "When in Rome, ..." and all that seems to apply (Microsoft is, after all, an American company).

It is also a global company!

I have checked in the .NET Framework Developer's Guide  under the section Best Practices for Implementing the Event-based Asynchronous Pattern and it asserts that "In the case of cancellation, set the Cancelled flag in the AsyncCompletedEventArgs object".

Which guideline has precedence?

If you would like to override this behaviour for a particular term, simple add the term to the <Unrecognized> element of CustomDictionary.xml. For example, with the following section:

  <Unrecognized>
   <Word>canceled</Word>
  </Unrecognized>

...this warning will not be raised when "Cancelled" is encountered.