They are retired and reissued. At the current share price they have to issue a lot more shares. But if they have the money then they don't have to reissue them.
So, the last time they retired 1.2M shares and reissued 2.4M shares (because the share price was lower, or the contract bigger). I don't expect a reduction in O/S in the near future. Perhaps later this year.
News 
Market Data 
Discover 
