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