sad to see this... and how about the back of lens?

I got this lens from ebay recently and found out this lens was a bit different from my other pentax collections. I have never touched the M series and on this lens, there's no glass near the lens hood which is not found on my A, FA, DA lens. I dun know if it's been customized to be like this or it's for some other reasons? Many thanks in advance and sorry about my poor English.