Why service behaviour 'releaseserviceinstanceontransactioncomplete = false' is required with 'concurrencymode.multiple' on transactions enabled

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WCF

One of my WCF service operation has transaction enabled-

[OperationBehavior(TransactionScopeRequired = true)]
public Car UpdateCar(Car c)
{
}

Earlier, I was running this service with InstanceContextMode as PerCall and ConcurrencyMode as Multiple which was getting me the below error-

An unhandled exception of type 'System.InvalidOperationException' occurred in System.ServiceModel.dll Additional information: The 'InventoryManager' service is configured with ReleaseServiceInstanceOnTransactionComplete set to true, but the ConcurrencyMode is not set to Single. The ReleaseServiceInstanceOnTransactionComplete requires the use of ConcurrencyMode.Single.

What I have tried:

In order to solve above error, i set 'ReleaseServiceInstanceOnTransactionComplete' to false and this did the trick.

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall
                 , ConcurrencyMode = ConcurrencyMode.Multiple
                 , ReleaseServiceInstanceOnTransactionComplete = false)]

Can someone please help to understand how disposing the service instance with 'PerCall' and 'Multiple' case solved this problem. What is the problem WCF thinks if I release service instance.