Exchange (2007/2010) Sync

I have two Exchange accounts (one on a 2007 server and one on 2010). For both, if I delete email in Outlook it'll eventually go away on my phone automatically but the inverse isn't true. If I delete from my phone, even hours later the message remains in Outlook. If I manually hit the Sync option then everything clears up as expected, but shouldn't this happen automatically? I have the download option set to as items arrive and this has occurred since RTM up through Mango (just upgraded yesterday).