Video (XDCAM codec) plays on QT-X but not in Cubase6.5

I am working with a XD-CAM HD video file that plays fine using QuickTime X (but whitescreens with QT7 Pro). In Cubase 6.5 I can import the file, audio is fine, but video window whitescreens. (MAC OSX 10.7.4)
Obviously QT-X has the codec to play the file successfully, but somehow Cubase is unable to use it. I have tried the trial version of CalibratedQ’s XDCAM codec, which Cubase can use, but video playback freezes when I play from any position on the timeline other than the very beginning - so that is useless. (Perhaps performance improves if you buy it)
I realise I could convert the video, but it’s the strange fact that QT-X standalone, can play it fine that has me posting, because although QT-X has plenty of issues of its own, it seems that Cubase is missing this particular connection with the QT engine.
Anyone else experienced this?