This has been a problem for me for years.
Anytime I use Mobile Sync with Quicken Classic Deluxe, my account balances will randomly change after syncing. Sometimes by just a dollar or two, sometimes by hundreds of dollars.
I then have two choices; look for the discrepancy, which is nearly impossible as I'd have to go through years of transactions, or restore from a backup. But then if I continue using Mobile Sync, at some point it will change again. Why??