I've run across several spellcheck quirks over the years. Things that I have found to be hillarious. At one time, if I remember right Microsoft was not a valid word in either Outlook or Word's spell checker, and I laughed histerricly at it.
The one that I laughed at just moments ago while posting is "blogging" is not a valid word in Blogger's spell checker. I know it's a fairly new word and not in the established dictionary, but when you create a tool that's helping to lead the way in personal content online, and you practically make the phrase blogging a common action verb, you would think that you would add it to your own dictionary.