STDDEV, STDDEV_SAMP, STDDEV_POP functions definition error

Let's take a look at the relations between listed functions from different approaches:

MySQL:

STDDEV() = STDDEV_POP()

STDDEV() != STDDEV_SAMP()

Couchbase:

STDDEV() = STDDEV_SAMP() — There is difference in case of one row ( It differs from STDDEV_SAMP in that STDDEV returns zero when it has only 1 row of input data, whereas STDDEV_SAMP returns null.)

STDDEV() != STDDEV_POP()

Spec:

https://docs.google.com/document/d/1y4MDYI0R5nykSFJGOA4v0OSbg35YfPbaFUAvVq6vcRA/edit#heading=h.wpmh045jt8nd

STDDEV() = STDDEV_SAMP()

STDDEV() != STDDEV_POP()

Real life:

STDDEV() = STDDEV_POP()

STDDEV() != STDDEV_SAMP()

So, I think, STDDEV_POP() and STDDEV_SAMP() are messed in specification and in Couchbase backend. 

Same thing for VARIANCE(), VARIANCE_POP(), VARIANCE_SAMP() functions