I have same experience with this. I am using Local/XXX@context as dynamic agents for the queues and this is discovered :
If members are added as LocalXXX@context/n, after attended call transfer, the agent is still blocked until the call is ended between the callee and the transfered extension.
If members are added without "/n" suffix, then they are available immediately after the call is transfered.
But in both situations, there is no record in queue_log that the call is transfered.
Another thing, if I try to monitor ( online with ChanSpy ), than in the first case ( with "/n", the call can be monitored, otherwise ChanSpy connects to some non-existing channel and there is deaf line. To monitor the call, I have to ChanSpy the SIP extension directly instead of the Local channel.
This is, for me, problem with the asterisk PBX, some bug or probably problem with some parameter into the config files.