DDL Statements Fail Or Not When DML Active?

DDL statements automatically end with COMMIT the user transactions in which they appear. Foe example:

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create table mytable01 (i integer);
insert into mytable01
select 1 from dual;
create table mytable02 (i integer);
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After all three statements are executed, data are committed in mytable01.

In the Oracle DB server SQL guide we read:

"DDL commands, such as TRUNCATE, will fail if there is any DML command active on the table. A transaction will block the DDL command until the DML command is terminated with a COMMIT or a ROLLBACK."

But I executed the following without any problem:

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create table mytable (i integer);
insert into mytable
select 1 from dual;
commit;
update mytable
set i = 2;
alter table mytable add (j integer);
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So where's the truth? Are DDL statements blocked when they refer to an active object accessed from a DML or not?