I'm using a MacBook Pro (osx 10.5.8) w/Apple Motion 3.0.
I created a black rectangle shape and placed it in front of all other layers. I keyed the opacity to simulate fading to black, etc. Started making changes to other layers in the keyframe editor, then decided to change the keys of this black layer. All of a sudden that layer shows up as blank in the Layers window. It is unchecked, no longer displays a name, nor shows up on the timeline, and is unselectable/checkable. But it is still active...still fading in and out as I previously keyed!