The stable versions of media-plugins/mythdvd, media-plugins/mythvideo, media-plugins/mythweather and www-apps/mythweb (0.18.1) depend on a version of media-tv/mythtv (0.18.1) that no longer exists. Please either mask bring back media-tv/mythtv-0.18.1 or mask these previously stable packages.
0.18.1 is gone.... And the 0.18.1 plugins are going away. Security holes and tons of issues. And yes, that means there are no stable plugins..