Blend mode missing from some clips?

Hello!
I'm working on a short documentary (400 plus clips in the timeline!!) on fly fishing and have come across an oddity-
I did some color grade tests earlier this year using FCP7 and MB Looks which my producer liked.
Thinking I'd go ahead and use FCPx for the edit and try to emulate those looks is a bit daunting, but after installing Denver Riddle's Luster pack I'm getting pretty close. I had a talk with him yesterday about using the color board presets instead of the effects presets which only have an opacity slider. Anyway the top layer calls for a blend mode of screen. Most of the time it's an available option. Sometimes it isn't:unsure: ... Any clue why this may be??

I've not been able to reproduce this yet, but let's get some basic information to help out.

What is the format of the original clip?
Did you import it as native format or Optimized?
What other Effects have been applied?
What other Adjustments have been applied?

Hey Ben,
we shot this project with 5 and 7 Ds.
All clips were transcoded to prorez 422.
no adjustments. no transformations. and no dissolves.

the clip that was to have it's blend mode changed was reset to stock in the timeline after I duplicated from below.

I ended up using the show clip in events and re editing it back into the timeline.
must have been a bug.