In OS X 1P 4.3.1.BETA-3, my "All Items" total is 294. In iOS 4.5.1b2 (and recent earlier betas), it's 340. This discrepancy has been there for quite some time; I only just really focused on it.
I expect "sync" to mean "all copies have identical content (once the dust settles). Is that a misunderstanding?
I hunted down one of the 50 or so differences. It has some odd recent history:
With that history, I find that the Mac 1P has only the new entry, while the iOS 1P has both old and new.
Given the joys of Heartbleed, I can easily believe that the 50 or so "All items count" discrepancy is made up entirely of entries with similar history:
1PAnywhere/Dropbox (local to Mac, at Dropbox.com) agrees with the Mac.
1PAnywhere/Dropbox (iOS) says
Problem loading 1Password data file. A key data file could not be loaded and 1PasswordAnywhere cannot continue without it. Please see this help guide for troubleshooting tips.
The linked tips say to click on the linkified phrase "key data file" to see if the file is actually there. Clicking the link does nothing. Holding the link lets me copy the link target, dbcache://dropbox/392287/1Password/1Password.agilekeychain/data/default/encryptionKeys.js. iOS Dropbox has that file, 5.8KB, "modified 1 year ago". OS X Dropbox has that file, 6KB, modified 9/6/12 (a year and a half ago).