If re-logging into the client after logging out, you are unable to press Play to launch the client. I tried to reproduce, but was unable to. It might be related to downloading the patch the first time.
1. Login and download patch
2. Press Play
3. After client launches hit the X
4. Login again
The screen that verifies the game with the Mordekaiser background was in an inactive state. "PLAY" is grayed out and can't be clicked.