Syncing multiple devices with one Outlook will result in new and interesting issues. You found one of many such issues. Remember that few will do this because it's a tar pit of support.
The only advice I can offer is to backup your stuff just in case it all goes pear shaped.
Syncing my iPod today I get a
warning that 25% of my Outlook calendar would be changed. I'm running
version 4.2.1 and iTunes 10.4.0.80. I ck'd the net and there were 2
other posts with what looked like a higher version on the iPod. I also sync my iPad and didn't get the message. I sync both devices with my Outlook from my home computer using iTunes.