In the Final Cut Pro 7 manual is explained how to switch and cut video and audio items separately. At the end, it says:
However, independently switching video or audio angles breaks linking relationships between a multiclip’s clip items in the Timeline. After you perform the switch, only the audio item whose angle you switched remains linked to the video item.
Which is exactly what happen in my case.
How can I switch angle for a piece of audio once the relationship is broken in the timeline?