As far as I know the difference between the DA and DA-L version of the 18-55mm lens is that DA has metal mount and the DA-L has the plastic mount. So mine (DA-L) has the plastic mount.
The optical formula of the lens is what I'm not sure of. I think that because it came with the K-x, and therefore a more recent lens, it will have the optical elements of the 18-55 II lens. I havent read anything official to confirm this other than the dpreview link I just gave and here is another link discussing it:
SMC Pentax-DA L 18-55mm F3.5-5.6 Lens Reviews - Pentax Lens Review Database
Also the pentaxforums lens database gives the optical properties :
DA 18-55 I:
12 elements, 9 groups, 6 blades
DA 18-55 II and DA-L 18-55:
11 elements, 8 groups, 6 blades