New mobileme push stops working after long sleep

I have converted to the new Mobileme calendar, and have come across a problem with push. Under most circumstances, events added on my iPhone or other Macs appear pretty quickly in iCal, which has the caldav account set to push. However, I sleep my Macs overnight, and leave iCal running. When one wakes up, I can see iCal refresh the caldav account and anything added while asleep appears fine. However, from that point on, push stops working completely. No events added elsewhere ever show up. I have to quit and restart iCal, then push starts working again. This is entirely reproducible on multiple Macs.

I can theorise that the session iCal must create with the Apple servers to receive pushed notifications disappears when the Mac is asleep for a log time, and iCal just doesn't recreate it when the Mac wakes up. On one occasion, when I quit and restarted iCal, the following message appeared in the console:

iCal[6210] We found a change that was not notified through push. Reverting back to polling for account with name xxxxx xxxxx

and after that push worked. However, I've only seen this message once, but always quitting and restarting iCal made push work again (but that's a pain).

Anyone else seen this? Seems like a pretty obvious bug to me.