don't know if it's a known issue.
my client failed to sync blocks at block 9661.
from the logs, switch fork failed because of detected duplicate transaction
20140711T010615.408801 th_a switch_to_fork ] switch from fork 76fdaa3232590335bace099a977c31a36327a4ef to c91e6df277471ad7654273370452f783e78c9cb5 chain_database.cpp:497
20140711T010615.408824 th_a get_fork_history ] chain_database.cpp:842
20140711T010615.408899 th_a get_fork_history ] return: ["c91e6df277471ad7654273370452f783e78c9cb5","3c5a66fe4b06a2b7798d8c167bddf472d3dc847a","76fdaa3232590335bace099a977c31a36327a4ef"] chain_database.cpp:863
20140711T010615.408930 th_a switch_to_fork ] extend 3c5a66fe4b06a2b7798d8c167bddf472d3dc847a chain_database.cpp:507
20140711T010615.410323 th_a apply_transactions ] Applying transactions from block: 9662 chain_database.cpp:517
20140711T010615.410544 th_a extend_chain ] error applying block: 30007 duplicate_transaction: duplicate transaction
{"trx_id":"12c892efad26a84c73a9271d2b0469b99645d7fe"}
th_a transaction_evaluation_state.cpp:189 evaluate
{"trx":{"expiration":"20140710T094537","delegate_slate_id":null,"operations":[{"type":"withdraw_op_type","data":{"balance_id":"XTSJa6bm5iPYsahikNECLr2k17gwWicnEUjm","amount":10000,"claim_input_data":""}},{"type":"withdraw_op_type","data":{"balance_id":"XTSBmdRD4rigXPmn6VjJVdydaNnq15SfzzAm","amount":10000,"claim_input_data":""}},{"type":"deposit_op_type","data":{"amount":10000,"condition":{"asset_id":0,"delegate_slate_id":7694373846492465735,"type":"withdraw_signature_type","data":{"owner":"XTS6gvyPkLeERzaNuP1JR5vrdW54skHzHJ56","memo":{"one_time_key":"XTS7D5HyiW6wPbHNbYzhYRhRG1hTfeBrDcHTm1W9Pq6VPHAg6hLLP","encrypted_memo_data":"d89b7e926009b356d23df76860e902952d435b0df62db29d723fdee18f916cd25ea576a06ecfddeeb8b34c70953b17d6f873e6c661a5ad534feb8f5d4f85a62f"}}}}}],"signatures":["20d7aee2566b2513d5d6f5ae3681c0e5fe9db4331343dd9e8e9e1cae61fec6c14ce053116fcf6744c946646cd1c7df4172e5cec953ef0246d02d92f4c69a518f6a","200a5d7c7fa6d90f1d6c71edca6c0da55e74ad1cc60a6feb212c8aec15d34ab631a2e5cdc159f52df64058166250d439f8c3ab258ca308eb659119bbf55b469fbc"]}}
th_a transaction_evaluation_state.cpp:218 evaluate
{"trx_num":0}
th_a chain_database.cpp:550 apply_transactions chain_database.cpp:817
20140711T010615.549060 th_a push_block ] attempt to switch to fork failed: 30007 duplicate_transaction: duplicate transaction
{"trx_id":"12c892efad26a84c73a9271d2b0469b99645d7fe"}
th_a transaction_evaluation_state.cpp:189 evaluate