According to http://www.united.com/web/en-US/apps...omoCode=A15099

There is a promotion running for award travel within Japan. I can't however book ANY flights within Japan from Tokyo (NRT or ITM) to any destination within Japan for either money or miles. I've tried using both the 'old' and 'new' United sites and chrome and IE both logged in and incognito and get the same results. A sample booking attempt (with either flexible or set dates) between Tokyo and Sapporo yields: 'United does not offer service between Tokyo, JP (TYO - All Airports) and Sapporo, JP (CTS). Please modify your search criteria'.

BTW, specifying HND or NRT instead of all airports gives the same indication.
I've reported this to United...but who knows this could be a feature instead of a bug or else something very odd with my account/computer.

Is anyone else seeing this behavior?