When I create a Cylinder with say 20 subdivisions, it doesn't matter how many because my extrusion will have 12, always 12. Maybe that helps to your guys search for the solution to my problem.

Greetings Brecht

Edit: I was a little wrong about this:
When I create a 12 subdivision cylinder and then use extrude face the extrusion comes nice together with the lines of the unextruded part =p. When I create a 20 subdivision cylinder there are more subdivision in the extruded part, but I don't know what's wrong, I guess less subdivions or something like that, anyhow, you guys are the pro ones.