Disk Allocation Problem with aiff file

[Talisker]

This was the problem: I downloaded a playback file which came in aiff format and used it in a session. The playback file was sitting on the desktop as well as in the audio folder of the session. However when I removed it from the desktop pro tools couldn' find it in the session audio folder even after trying to manually link it. Only when I reimported it from the audio file folder back into the session by just dragging the file onto a new track, it was finally being recognized.
Does that have something to do with the format of that file or is there another explanation ?
thanx for info