Should be straight alpha, but it doesn't look like it

Question

I'm using Keylight on some footage in AE CS4, and then bringing it into PPro CS3 for the rest of the editing process.  In AE, one of my roses (a light one chosen to accentuate what is going on) looks like this:
I have "Unpremultiply" checked in Keylight, and here are my Output Module Settings for the render:
As far as I can tell, I should be doing everything right to end up with footage with straight alpha, but in PPro, I get the famous "premultiplied-alpha halo" anyway!  At first, the halo was only appearing a second or two after I would click in a new spot on the timeline - that really got my attention that it was something other than just bad keying on my part.  I actually tried to catch a screen capture during that moment before the halo would appear (to show the before-and-after), but by the time I decided to try that, Murphy's law had kicked in - now there is no delay and it looks like this all the time:
I have several roses that I have processed in the same manner, and they all have the halo, but it's of course not as obvious if the rose itself and/or the background footage is darker.
I'm pretty new to keying and alpha, but I thought I had done my homework, so to speak.  What other settings should I check?

Answer 1

Thanks for the suggestion - it basically worked.  PPro CS3 doesn't appear to have an effect called "Alpha Key", so I used "Track Matte Key", specifying the track where I put the alpha clip and selecting Luma Key for the setting (setting it to Alpha Key didn't do anything, and it was clear that the "alpha" AVI was not an alpha channel per se, but just a regular video clip with a B&W representation of the transparency).  I also don't see any effect called "Minimax".  Anyway, I followed your suggestion as best I could with the tools I have - you must be using a newer version of PPro.  I can indeed see about a pixel or so that would be better if it was more  transparent - I suspect your Minimax suggestion would have taken care of  that.  But this is definitely usable.
Key point for those reading this later: You have to choose "Straight" for the Color setting when you render by this method, even though you get some strong warnings that dissauded me the first time I tried it (I thought they were saying I had to include an alpha channel in the stream, not the method I was about to use).
One more question: When rendering the separate alpha clip (essentially just a grayscale video of the transparency) to be used as the luma matte for the Track Matte Key, does it matter whether the Color setting is Straight or Premultiplied?  I can't imagine that it would matter for that clip, but if there is a subtle difference, let me know.
I have no idea why I can't get it to work with an embedded alpha channel, though - surely hundreds or thousands of people use these two programs to handle RGB+Alpha video files.  For this time, I'll re-render my roses (twice for each rose to get the two streams - this will give my CPU a workout!) and use this workaround, but if someone has any insight about the more direct method, please enlighten us all.