The urge to pee after ejaculation is common in many guys. Although I don't experience that sensation.
However, I have noticed that if I try to pee after I cum, it is very difficult for it to flow out at first. Its like the ejaculation muscles are still in contraction mode, and constricting my urethra, and when they feel something in the urethra, they still think its cum, and try to contract and make it spurt out instead of letting flow. It's like it takes the brain a few seconds to realize that this isn't cum any more, and that its OK to relax everything down there and let the pee flow out unrestricted.
<i>My avatar is a picture of my own sperm under a microscope. Pretty cool huh?</i><br />Drugs are garbage. I'm high on my own testosterone.