The bug has been opened on https://bugs.launchpad.net/ubuntu/+source/rhythmbox/+bug/136604

"Binary package hint: rhythmbox

Description of the problem:
When a computer is actively streaming music to other machines over DAAP it is inconvenient to keep poking it to prevent it from automatically turning itself off.

Steps to reproduce:
(Assuming you're on AC power and you have imported some music e.g. /usr/share/example-content/ )
1. Start
gnome-screensaver-preferences .
2. Set "Regard the computer as idle after" to 1 minute.
3. Start
gnome-power-preferences .
4. In the "On AC power" tab set the "Put computer to sleep when inactive for" time down to 2 minutes.
5. Start
rhythmbox .
6. Within rhythmbox go to Edit -> Plugins.
7. Within "Configure Plugins" ensure that DAAP music sharing is ticked. Click on the Configure... button.
8. Tick "Share my music".
9. Click Close and then Close again.
10. Use another network computer to start streaming music from the original computer via DAAP.
11. Don't touch the original computer for 2 minutes.

Expected result:
Screen on original computer to dim and be blanked, music in the midst of playing on second computer to continue playing.

Actual result:
Original computer's screen dims but around a minute later music will stop being streamed as it goes to sleep.

Additional information:
If music has never been streamed, has not actively been streamed in the past two minutes or DAAP is turned off then autosuspend should not be inhibited by rhythmbox (unless it is in party mode).

Version information:
Ubuntu Gutsy (development branch)
rhythmbox 0.11.2-0ubuntu2
..."