Just picked up a 4536 in very good shape for $359. Yay me. It came with 3 mags. 2 mags are marked "This magazine must have a yellow follower." The third has the above mark, and also has "only for use in 4516-1. Not for use in 4516 or any other revision of the 4516." Whats the deal with these magazines? Just curious really, never seen them marked like that before.