ActiveSync and power settings

It seems that the power settings on the device ("On external power" : "Turn
off device if not used for xx minutes") isn't being used when the device is
also running ActiveSync.

I can have the device running on batteries or external power and have it
shut down (hibernate) as specifed in the power settings but as soon as
ActiveSync is running then the device doesn't power down.

I understand that I would then have to re-activate the device for ActiveSync
to sync again but that's exactly the behavior I'm looking for...

Any insights as to why ActiveSync seems to disable the power settings or any
workarounds ?

/Peter