is probably due to the fact that the certificates of the converted debentures have been mailed out to clients therefore they might be selling some shares that they previous had in there account from previous holdings.
So lets say that a person received his certificate for 100,000 convertable debentures that he can't sell until dec.1. Now lets say that he has 100,000 shares in his account that he accumulated over the past 3 months. Instead of waiting to dec.1 to sell some converted debentures, he sells some of his accumulated shares.