Doesn;t sound like you are doing anything wrong and the media browser (which is what I assuming FCP X uses to get the Aperture images) should show all versions of an image.
You're Aperture terminology is a bit off. In Aperture all you ever see are versions unless you specifically ask to see the master and the media browser isn;t able to access the masters. So in this case you described you have two versions, one that Aperture created when you imported the image and the second one you created via some command (new version from master or duplicate version).
So when you say you changed the version name of thw master it sounds like you renamed the first version that Aperture created.
One thing to try open another iLife program , mail is a good choice. Now create a new message and in the upper right hand comer of the mail message you'll see the icon for the media browser. Open it and look at the Aperture library. Do you see both versions of the image?
Not sure if this will help or not but: I was updating a version in Aperture by cropping it. I noted that FCP X was not updated in my media browser and initially thought it was something to do with the preview. I then noted a check mark over my original version that I had duplicated in order to conduct the crop. I realized that the two versions were "stacked". After extracting the new "cropped" version from the stack, it showed up in my FCP X media browser. Just another thing to try.