Locking issue SAP CRM 4.0 and SAP R/3 ECC 5.0

Hi all, I have a problem that I would like to share before creating any OSS message. I have connected our CRM 4.0 environment to our new SAP R/3 ECC 5.0 environment and am faced with a strange problem. All middleware settings seem to be correct, business partners, products, pricing and all are replicated correctly. However when I create a sales document in CRM it gets replicated to R/3 correctly but it remains locked by my RFC user, preventing me from making changes to the replicated document. The BDoc status remains 'in process' and for some reason the lock is not being removed. Does anyone have seen a similar situation and how was it solved? Thanks, Tiest.