I went to the Kindle management web site and noticed that whispersync is turned off (via these instructions:
http://www.amazon.com/gp/help/custom...deId=200775230 ) . I'll have to see if it was actually synching or not.
In the meantime, I'm chatting with Kindle support.
UPDATE: They had me try a factory reset but that didn't improve the situation. They said they would have to email me when a resolution is found.