Hey guys i figured out the recurring-sync issue, can duplicate and fix on demand (so can you). The problem occurs when your setup to sync with a social networking site (IE FaceBook) and you remove the FriendStream application.
The reason it's happening is because when you setup for social networking such as FB, its set to not only sync contacts, but also live feeds, those live feeds are directed through the friendstream app, so even if you don't think you're using friendstream .... if your setup for social networking you use it.
Test: (for this example to work, don't be setup on any other social networking site because im using FB for an example but any of them will do it)
1. Setup for FB. There are a couple ways to accomplish this but an easy way is Menu > all apps > setup > skip > next > next > tap facebook and setup your account.
2. Delete the friendstream apps. Menu > all apps > settings > applications > manage applications
3. Now sync. Go to Menu > all apps > settings > accounts & sync > select "sync all"
4. Sit and watch the sync logo spin at the top of your screen, it will never stop so go to the next step when you get bored

5. Now click cancel sync (still in the accounts and sync screen)
6. Select the facebook for HTC sense (still in the accounts and sync screen)
7. Remove check mark from "sync live feeds"
8. Hit back button then select "sync all" ... should finish within a few seconds.
9. Wanna watch it happen again? Go back in and turn on "sync live feed" for facebook then "sync" .....
Fix:
A) Don't remove friendstream if you use social networking
B) If you want to use social networking AND remove friendstream, make sure you uncheck "live feeds"