I saw a video on flirting, I think that Wolfheart posted it somewhere on WP. They had single men and women mingle in the hopes of finding a date, then watched the body language. They would show the ways in which the females were flirting, and how the men reacted, or flirted themselves. In an interview afterwards, the men were sure that the women were flirting. But when the women were asked, they would deny the flirtations.
Moral of the story, I believe that many women flirt without the intention of showing interest.