It is especially frustrating when you talk with people. You accidental move camera off screen and can't back because there is this screen movement lock.
If there are UI elements in the way of moving the screen with the mouse, you can use WASD to move it (as long as the mouse cursor isn't over a UI element), or hit Home to re-centre it on the lead character. Normally you can use the arrow keys to move the screen, as well, but only the left and right arrows work for that during a conversation.
