Who's a maverick?

From vice-presidential debate, Joe Biden on "the maverick":

Look, the maverick, let's talk about the maverick John McCain is. And again, I love him. He's been a maverick on some issues. But he has been no maverick on the things that matter to people's lives. He voted four to five times for George Bush's budget, which put us a half a trillion dollars in debt this year and over $3 trillion in debt since he's got there. He has not been a maverick in providing health care for people. He has voted against -- he voted against including another 3.6 million children in coverage that -- of the existing health care plan when he voted in the United States Senate. He's not been a maverick when it comes to education. He has not supported tax cuts and significant changes for people being able to send their kids to college. He's not been a maverick on the war. He's not been a maverick on virtually anything that genuinely affects the things that people really talk about around their kitchen table. Can we send -- can we get Mom's MRI? Can we send Mary back to school next semester? We can't make it. How are we going to heat the -- heat the house this winter? He voted against even providing for what they call LIHEAP, for assistance to people with oil prices going through the roof in the winter. So, maverick he is not on the important, critical issues that affect people at that kitchen table.

As Arthur Dent might say, This is obviously some strange usage of the word "maverick" that I hadn't previously been aware of.