At the lowest left corner of the timeline, drag the little button all the way to the big clock at the right so you can see individual frame ticks on the timeline.
In the preview window, verify that "clip" is highlighted. Press the "one frame back" button.
Back to the keyframe settings, click the little diamond again to make another keyframe, which will be set to 0% opacity, so the clip pops in at the in point.
When I do this, I do not get another keyframe on the timeline... until, of course, I am verifying this post. Then it works... sometimes.
I'll add more if I can figure out a pattern.
Does this sound familiar to anyone?
PD9.0.0.2504