Bug in iPod

I didn't know exactly what to call the event that occurred. That is why I am calling it a bug.

The problem:
Receiving a call on a mobile close to iPod increases the volume of song currently playing.

Steps to reproduce:
1. Make sure that some song is playing on iPod.
2. Keep the mobile on 'Vibration Mode'.
3. Keep your mobile close to iPod.
4. Ask your friend to give you a call on your mobile.

Expected:
Receiving call shouldn't affect your iPod.

Actual:
Volume gets increased.

Additional notes:
iPod used is iPod Video (30 GB) with latest software version (1.1.1)
Mobile used is Sony Ericsson K700i.
The song being played was from movie 'Rang De Basanti' (if that matters).

The problem could be reproduced by two different persons, three times.

Waiting for comments from different iPod owners.