Dave, thanks for responding.
Strange thing: in FCP X (and even in Keynote, with which I used to use Motion all the time), the alpha was working properly. But all the alpha options were grayed out in AE’s ‘Interpret Footage > Main…’ dialogue.
Stranger thing: I tried it again today, all the exact same settings, and now it works. The only thing I can figure is I may have had a blending mode set incorrectly in mFlare, but it was so late last night I don’t remember what I changed when.
Again, thanks for reaching out.
—AE (AKA “lookatthisguy” in many, many other places)