MP3 drifts out of sync.

A friend of mine is trying to edit some video/audio together where the audio was recorded using a Zoom H1 and the camera audio.

The Zoom recorded MP3. The camera recorded quicktime audio.

The camera audio is in sync with the video. But, the zoom audio drifts out of sync (with the camera audio and the video).

Is this a common occurence with MP3s? 

Seems pretty bizarre.