I saw a bug in DNNP-1985 reported by Jay Mathis otherwise known as the Child Portal Logout problem. This issue was withdrawn with a Won't Fix.....The issue has been around for a long, long time and someone has to do something sometime........

1) I do not believe this can't be fixed
2) If it can't be fixed, DNN should not have the ability to create child portals anymore.

There is a big, big, huge, major post on this issue in the forum, (see here) including members from the core (Cathal Connoly, Nina Meiers, Paul Davis, Chris, etc.). And after about a year it has still not been resolved.

It is a major bug for a lot of people which probably isn;t easy to solve, it involves cookies, cache,  friendly URL's, Membership stuff, etc. But I think this is really something you can't run away from any longer. You either have to solve this issue or remove the child portal concept from DNN. But do not say: Well, uuhm, it won't fix but we'll keep it anyway, bug or no bug. That is not a solution.