Preseed and bleeding?

Has anyone experienced bleeding after using preseed? We used it for the first time, on CD12 (I have a 27 day cycle), and a few hours later I had brown and pink spotting, with the occasional bright red. Lasted a few hours; light spotting lingered for two more days. It's too early for ovulation bleeding which I never have anyway, so I'm at a loss for why this is happening. Could it be a reaction?