Cisco VPN :: ASA 5500 - IKEv1 HASH Payload Length 4 During QM 3?

I connecting to a Cisco ASA 5500 using a third party IKEv1 client. The initial connection and all rekey attempts that start on the client are successful. A tunnel is established, data cna be transferred between the client and the ASA's internal network etc.However, when the ASA initiates rekeying of a Quick Mode SA this is rejected on the client. The rejection occurs due to QM3's HASH payloading having a length of 4, which is wrong.
 
ASA log:
  
ISAKMP Header
  Initiator COOKIE: 48 81 9e 1b 80 94 41 a9
  Responder COOKIE: fa ab 87 c7 a5 d9 8d 35
  Next Payload: Hash
  Version: 1.0
  Exchange Type: Quick Mode

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Since the initial negotiations work, pre-shared key, IKE/IPsec settings etc should be correct; if they weren't the connections wouldn't work in the first place.