[Help] The Opacity changes when the background clip ends?

This is a little weird. I have a clip in v4 that is fading out (using key-frames) and a clip in v5 which is fading in. They are overlapped at the end of the v4 clip and as soon as the v4 clip ends the v5 clip, which was fading in, becomes more opaque.

This album shows more clearly what's going on.

http://imgur.com/gallery/5Ux8m

There aren't any stray key frames in v3, it happens regardless of whether or not the v2 clip fades out or just ends, and it happens regardless of the order that they are stacked.

Maybe it's something silly. Any ideas?