In the current implementation of the Raiden protocol, when a payment routing fails after some transfers, the already made hash time locks are left there until they expire. This consumed the channel capacity for quite some time. (The situation doesn't change whether or not RefundTransfer messages are sent.)
I think it's possible to free the channel capacity immediately (e.g. by adding removed lockhashes in the other side of the channel state). Is there a reason behind the current design?