missing mutation from backfilled stream request

from test: test_stream_request_dupe_backfilled_items (pyupr)

Create 2 keys and loads 3 duplicate copies of each so that the first time I request these items they are on seqno's 3, 6 :
....

{ 'key': 'keya', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 3} {'snap_start_seqno': 4, 'flag': 'memory', 'vbucket': 0, 'opcode': 86, 'snap_end_seqno': 4} {''key': 'keyb', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 6}

• these are all in-memory snapshots

The test continues to do the same stream request until disk snapshots are returned, but this time I only get seqno 3 and then a snapshot at seqno =7.

{'snap_start_seqno': 0, 'flag': 'disk', 'vbucket': 0, 'opcode': 86, 'snap_end_seqno': 4} {'key': 'keya', 'flags': 0, 'nru': 2, 'vbucket': 0, 'by_seqno': 3, 'rev_seqno': 3} {'snap_start_seqno': 7, 'flag': 'memory', 'vbucket': 0, 'opcode': 86, 'snap_end_seqno': 4}

• didn't get 'keyb' this time, it's the same request as the last one.

There's a side-effect there in Snapshot Response where this is causing snap_end_seqno > snap_start_seqno.

-Tommie