iMac won't go to sleep after 'wake for network access'

Hello,

I know this question has been discussed in part in other discussions, but I cannot find someone with exactly the same problem as me. So here it is:

On my iMac, I've turned on 'Wake for network access'. This way, I can wake up my computer over wifi from Apple TV or iPad to access iTunes content. This works fine.

The problem I'm having is that the iMac won't go back to sleep after that.

I've narrowed down the problem to the 'Wake for network access' parameter. If I turn it off, the iMac goes to sleep according to the settings in the 'Energy Saver'. If I turn it back on, the machine stays on indefinitely.

I imagine this is not normal - surely there's a way to use 'Wake for network access' AND have your computer going to sleep when you don't use it.

Has anyone encountered a similar problem? Any workarounds?

NB: I'm looking for a solution that allows me to keep 'Wake for network access' on.

Thanks in advance for your help.