HI,
This does seem to be a cross between a server issue and Messages itself.
However it could also be one of those things that can be "fooled" by the Force Quitting of the IMTransferAgent.
Most people seem to report the issues arises for them if the Messages app is Off line when the Pics are sent or Asleep.
This suggests the Server can't tell what has been sent and what should be synced.
Of course one view would be the app can't tell if it is new or synced stuff that is being sent.
10:10 PM Thursday; September 13, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously