I'd say that all men do...but I wouldn't say that it's a problem. It's just the nature of the beast. Depends on far too many variables to enumerate: energy, horniness, source of stimulation, etcetcetc..... As for the relative lack of kick with partial-erection orgasms, the penis is physiologically constructed and wired to perform at its orgasmic best while at its maximum hardness (= maximum length)...evolution's way of enabling deep penetration to increase the likelihood of insemination. I doubt that Nature has too much interest in masturbation.