Replace on a locked doc gives Key not found error

Using the python SDK a customer has discovered that replacing a value on a locked document results in a key not found error. Mark Nunberg investigated from the SDK perspective and determined that the server is returning this incorrect error.

Example:
python
Python 2.7.8 (default, Oct 19 2014, 16:02:00)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.54)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from couchbase.bucket import Bucket
>>> b = Bucket('couchbase://localhost')
>>> b.upsert('x', 'value1')
OperationResult<RC=0x0, Key=u'x', CAS=0x44c778fbec280000>
>>> b.replace('x', 'value2')
OperationResult<RC=0x0, Key=u'x', CAS=0x2906244eee280000>
>>> b.lock('x', ttl=30)
ValueResult<RC=0x0, Key=u'x', Value=u'value2', CAS=0xb5784741f0280000, Flags=0x2000000>
>>> b.replace('x', 'value3')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "couchbase/bucket.py", line 401, in replace
persist_to=persist_to, replicate_to=replicate_to)
couchbase.exceptions._NotFoundError_0xD (generated, catch NotFoundError): <Key=u'x', RC=0xD[The key does not exist on the server], Operational Error, Results=1, C Source=(src/multiresult.c,282)>
>>> b.upsert('x', 'value3')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "couchbase/bucket.py", line 361, in upsert
persist_to, replicate_to)
couchbase.exceptions._KeyExistsError_0xC (generated, catch KeyExistsError): <Key=u'x', RC=0xC[The key already exists in the server. If you have supplied a CAS then the key exists with a CAS value different than specified], Operational Error, Results=1, C Source=(src/multiresult.c,282)>
>>>