Version:            (using KDE 4.2.3)
OS:                Linux
Installed from:    Fedora RPMs

In KDM if you select a session type that differs from your last session (e.g., were running KDE, now want to run Gnome) and then entered your User ID and password, it runs KDE again instead. The problem is that as soon as you put in your user ID, it resets the session type selection to the previous session type for that user, regardless of what was just selected.

Actually, gdm does the same thing. However, with it you can see at the bottom of the screen that the act of entering your user ID has changed the session type back to what it was. You have to be watching pretty close with gdm but at least you can see that it changes. With kdm, unless you already know what it is doing, it can seem like it will not switch your session type even though you just selected a new one (because the state of the session buttons are not visible unless you open it up and look).

See https://bugzilla.redhat.co/show_bug.cgi?id=502953 
for additional discussion of this "bug". (Maybe this is halfway between a bug and a "wish"?)