I work at a facility that has lots of After Effects stations. All of the computers with 10.0.1.19 have the same problem that you are noticing. The 3 stations that were not upgraded, 10.0.0.458, play XDCam EX just fine. All of the Quicktime Components are the same. We are hoping that the next upgrade will address the issue.
A slight aside question. I am from an editorial background and understand the importance of choosing a good editorial codec. For After Effects though, does it matter to transcode video files out of a lossy codec and into a more uncompressed codec? Isn’t After Effects only rendering once anyway? Obviously there is no other solution here, but in general.
Brian