Bug with autocommit=0 and SET TRANSACTION?

[Johnny The Frog]

I am currently reading up about MySQL locking and transaction isolation levels and doing some very basic tests in this field to get a full understanding about how it all works. Using MySQL 5.5 and the InnoDB engine, I have found the following problem:

Citing from section 14.5.2 of the manual: "If autocommit mode is disabled within a session with SET autocommit = 0, the session always has a transaction open."; citing from section 13.3.6 of the manual: "SET TRANSACTION ISOLATION LEVEL without GLOBAL or SESSION is not permitted while there is an active transaction:".

Thus, the following should NOT work:

mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)

mysql> set transaction isolation level serializable;
Query OK, 0 rows affected (0.01 sec)

But it DOES work. This is probably a bug because (according to the manual) an unfinished transaction is active as soon as you disable autocommit, but the second statement should fail if a transaction is active.

Unfortunately, I don't have the means to test this for 5.6 or 5.7.

I would be very interested into thorough explanations.

Thank you very much in advance for your time and effort,

JohnnyTheFrog