recvd snapshot twice during failure scenario

wrote a script to perform the failure scenario here: https://github.com/couchbaselabs/cbupr/blob/master/failure-scenarios.md

the gist of it: https://gist.github.com/tahmmee/11301024 (also attached)

At the end there is an attempt to stream 10k items.
However, what I'm observing is a snapshot is sent and after this a repeat of mutations at seqno_1.

Here is the stream response ->

{'status': 0, 'body': '', 'opcode': 80} {'status': 0, 'opcode': 83, 'failover_log': [(68675663887800, 1222), (55655994587054, 0)]} {'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key17', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 1, 'rev_seqno': 1}

...

{'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key9976', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 1224, 'rev_seqno': 1} {'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key9982', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 1225, 'rev_seqno': 1}

...

{'vbucket': 0, 'opcode': 86} {'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key17', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 1, 'rev_seqno': 1} {'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key21', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 2, 'rev_seqno': 1} {'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key24', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 3, 'rev_seqno': 1}

...

The last seqno sent is 1225, and in logs it shows this was where backfill completed:

[ns_server:info,2014-04-25T15:53:54.574,babysitter_of_n_1@127.0.0.1:<0.85.0>:ns_port_server:log:169]memcached<0.85.0>: Fri Apr 25 15:53:54.372982 EDT 3: (default) Scheduling backfill for vb 0 (0 to 1226)
memcached<0.85.0>: Fri Apr 25 15:53:54.373173 EDT 3: (default) UPR (Producer) eq_uprq:failuerscenario1 - Stream created for vbucket 0
memcached<0.85.0>: Fri Apr 25 15:53:54.377299 EDT 3: (default) UPR (Producer) eq_uprq:failuerscenario1 - Backfill complete for vb 0, last seqno read: 1225

I've attached the script with it's deps and it can be unpacked and reproduced in cluster_run:
./cluster_run -n4
python uprfailurescenario.py
...
AssertionError: ERROR: Out of order response on vbucket 0:

{'value': 'val', 'lock_time': 0, 'opcode': 87, 'expiration': 0, 'key': 'key5', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 1, 'rev_seqno': 1}