Background is supposed to be transparent - but its not!

Question

I am doing an NTSC DV project, 720x480.
Its just a simple lower 3rd.
When I right click the background Project Properties... its says "transparent" (not "solid") for background which is what I want.
However, when I export, I export as Apple ProRes 422 HQ NTSC (which I find is best quality).
When I import it into FCP, the background is SOLID black. So the transparency is being lost.
Why? How can I preserve transparent background? I looked in the ProRes422 options before export and tried exporting color+alpha etc etc, but can't find an option that respects transparency.
Help!

Answer 1

Hmmm, just tried Animation... still black. :s
Here's my presets:
Project is NTSC DC
Project properties:
Preset: NTSC DV
W,H: 720x480
Bit depth: 8
Pixel Aspect Ratio: NTSC D1/DV 0.90
Field Order: Lower first
Frame rate: 29.97
Background color [black]
Background: Transparent
Render settings:
Samples 8
Shutter angle 360
Exporting in ProRes422
Compressor: Animation
Col Depth: Millions
Quality 100%
Frame rate: 29.97
Key frame rate: 0
Sample size: 16
Channels: 2
Resolution 7820x480
Color: color+alpha
Premultiply : on
etc...