Functions Immutable but not parallel safe?

There's 11 functions which are marked immutable, but are marked as
parallel unsafe.

postgres=# select proname from pg_proc where provolatile = 'i' and
proparallel = 'u';
proname
-----------------------------
_pg_expandarray
_pg_keysequal
_pg_truetypid
_pg_truetypmod
_pg_char_max_length
_pg_char_octet_length
_pg_numeric_precision
_pg_numeric_precision_radix
_pg_numeric_scale
_pg_datetime_precision
_pg_interval_type
(11 rows)

I'm finding hard to imagine a reason why these might be unsafe, but
failed. I do notice they're all only used in information_schema.

Could it just perhaps be that these just missed the verification
process the other functions went through to determine their parallel
safety?

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services