In the "Other Settings" step, the list of window managers contains: "Gnome, Xsession, fluxbox". Thsi is neither a complete list of all window managers in portage neither based on the previous steps (I choose only to install KDE).
Then you should select kdm as the login manager. KDE is hard to set to boot using XSESSION because the versions change so often. Please learn a bit more about Linux before posting these bugs.
I know enough about Linux, thank you. I'm using it almost exclusively for over 10 years.
And KDE has new releases far less often than Gnome. If you want less SLOTS (personally I would prefer if the slots were only for the major version) than talk to the Kde Herd.
Both DISPLAYMANGER and XSESSION are ComboEntry fields. You can choose one from the list or enter your own. Not a bug.