Your shares might have been loaned out for short sale. If you buy shares in a margin account they can be loaned since you don't actually own them all. They are providing you margin. Obviously both holders can not vote them. In fact I think they could borrow your shares in order to short sell them, not sell them short, vote the rights, then hand them back. There is a cost of course for the borrow (which your broker receives as income). The cost would be low if they were not borrowed for long.

There were over 600,000 shares short earlier in the month.

http://www.investopedia.com/ask/answers/05/shortsalevotingrights.asp

These are well known accepted rules of using a margin account that are nothing new.