Identity columns, DEFAULT keyword and multi-row inserts

Hello,

assume the following table:

create table test
(
id integer not null generated always as identity,
data integer not null
);

The following insert works fine:

insert into test (id, data)
values (default,1);

However, a multi-row insert like the following:

insert into test (id, data)
values
(default,1),
(default,2);

fails with:

ERROR: cannot insert into column "id"
Detail: Column "id" is an identity column defined as GENERATED ALWAYS.
Hint: Use OVERRIDING SYSTEM VALUE to override.

My question is:

* If DEFAULT is not allowed for identity columns, then why does the single-row insert work?
* If DEFAULT _is_ allowed, then why does the multi-row insert fail?

The above happens with Postgres 10,11 and 12

Regards
Thomas