Adding beginning keyframe negates adjustment layer effect in premiere?

I'm trying to do an exposure transition between two clips using the Levels effect applied to an adjustment layer.

When I change the (RGB) White Input Level without any keyframes (or even just one keyframe) it works just fine:

BUT as soon as I try to make the level change gradual by adding the first keyframe at the normal White Input Level (255) it negates the effect?

Anyone know why? Or how to fix it?

I could just apply the levels effect to the clip and go with that, but this type of transition has worked before and It's a lot easier to just duplicate the adjustment layer than to manually adjust the beginnings and ends of clips each time I want to use it.

I've tried to change the opacity blend mode, I've tried to apply it to other clips.. I've even tried it with different Level's effects (RGB levels and Black Output) and nothing is working..

thanks!

-ben.