Solution to iPod Touch Podcast Sync Problem
*The intermediate solution:* Create a smart playlist on your iTouch called "Podcasts" where "Podcast is true." That's the only rule you need and in that new podcasts you will see all of your invisible podcasts you copied
*Why this happens:* The podcast section on the iTouch only will show UNPLAYED podcasts, once they are played, they "vanish" but really they are just invisible (unless you have that smart playlist). This is obviously a glitch to be fixed in either the next iTouch update or iTunes update. In order to delete unwanted Podcasts, you must go into the smart play list and delete them from there.
I HOPE THIS HELPS!
MacBook (1.83GHz Core Duo), Mac OS X (10.5.5)