ICal lost end dates and ∞ sync conflicts after iOS4 upgrade

Question

   After upgrading my sacrificial iPod 3 (I’m waiting to upgrade my main iPhone 3GS) and synchronizing it to my home MacBook Pro 2007 17", I got huge numbers of old repeating meeting which seem to have lost their end-date, e.g., “Palm-size PC Porting Lab” on June 28th this millennium, which I assure you is an error. I restored from a desktop backup, overwrote the iOS4 Calendar data, and synced again.
   After that, I had a miserable day full of a dozen or so Resolve Sync Conflicts dialogs—sometime three or four in a row after a single, very slow, sync. Several times two sync processes used up all my real memory (using over a gigabyte, out of three) and once it even used up all my disk space (I had 29G free). I also had a few rounds of conflict on my work MacBook Pro 2009 13", synced via MobileMe.
   Some historical notes: My calendar data is quite large, going back to Newton days via PalmOS, and iPhone OS 3 never handled it properly, e.g., both search and over-the-air sync are broken on my 3.1.3 iPhone. MobileMe sync data also gets corrupted every few weeks. And “Palm-size PC” was Microsoft’s court-ordered renaming of their trade-mark infringing Palm PC.
Macaulay‘s Law of Software Upgrades:
“To think nothing of symmetry and much of convenience; never to remove an anomaly merely because it is an anomaly; never to innovate except when some grievance is felt; never to innovate except so far as to get rid of the grievance.”

Answer 1

Deleting my caches per http://support.apple.com/kb/TS2481, and restoring and rebooting a couple of times, seems to have shut up the warnings, at least for now, but there's still some data loss, e.g., two meetings on 6/21 and 6/22 don't show up any more on my main Mac, but do show up on both my sacrificial iOS4 iPod, and my real 3.1.3 iPhone. (I’m also having trouble with a Note failing to sync from my iPad, but I haven’t tried that yet since nuking my caches.)