Shedding when shampooing?

[LookingToLearn]

When I run my hands through my hair when it's dry, I don't shed outside of the normal one or two small hairs everyone gets. But when I shampoo my hair, especially I've noticed when I go over the crown of my head, I get a bunch of long hairs each time I brush through it. Like, let's say I brush through my hair once--I'll get five or six hairs, and they'll be longish ones, like this long: ________ or a little longer

 

And that happens EACH time I run my hair through when shampooing. But never when conditioning, and never when the hair is dry.

 

Note that I wear a vintage hairstyle, long on top (usually slicked back with Brylcreem) and short on the sides and back. Could that account for the shedding?