PARALLEL SAFE/UNSAFE question

Hi all,

I was trying writing my own parallel aggregation functions on 9.6beta2.
During that, we found a bit confusing behavior with SAFE/UNSAFE options.

Once a PARALLEL UNSAFE function f1_unsafe() is wrapped by
a PARALLEL SAFE function f1_safe_unsafe(), calling f1_safe_unsafe()
produces a parallel execution plan despite it implicitly calls
the UNSAFE FUNCTION f1_unsafe().

Is this intentional?

Please take a look at our example here:
https://gist.github.com/snaga/362a965683fb2581bc693991b1fcf721

According to the manual[1], it is described as:

> the presence of such a function in an SQL statement forces a serial execution plan.

so, I expected that calling UNSAFE functions should produce
a non-parallel execution plan even wrapped in SAFE functions.

Is this a sort of limitations? Is this working correctly as we expected?

Regards,

[1] https://www.postgresql.org/docs/9.6/static/sql-createfunction.html
-- 
Satoshi Nagayasu <snaga@uptime.jp>