There have been reports at WebmasterWorld, that I can personally verify, that Google has approved payment for AdSense publishers for the same dollar amounts less then 10 days apart.
Normally, one will see a payment approved date once a month (less if your balance does not reach $100 for a particular month). Here, people are seeing (I am also) two payments approved in the same month for the same exact dollar amount.
One person said they emailed Google and the response was we are "working to resolve the issue". But yet, they have not received the payment for two as of yet.
Seems like all AdSense publishers are seeing this, so I would just chalk it up to being a glitch. Someone at Google hit that Pay Button one too many times. :)