Hi there -
I ran into a bunch of trouble today with WP Membership not redirecting back to the site or activating new members after 2checkout purchase. The problem is described in this thread, near the bottom: https://premium.wpmudev.org/forums/topic/user-account-created-but-not-activated
I finally realized that I had activated the MarketPress plugin today. So, I deactivated and lo and behold, WP Membership started working properly again.
Since I'm a mediator and also want to use both plugins, I must ask: Is there a way to get these two to end their conflict?