SHOW GLOBAL VARIABLES ... autocommit?? What?

The autocommit variable is a session only variable, right? Easy to confirm by:
mysql> select @@global.autocommit;
ERROR 1238 (HY000): Variable 'autocommit' is a SESSION variable

But if I do this another way, I get a different result:
mysql> show global variables like 'autocommit';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit | ON |
+---------------+-------+
1 row in set (0.00 sec)

To me, this is a bug, right? But before I report it, I wanted to see if you agree, or? Might there be stuff out there that relies on this strange behaviour. And it gets worse, I'm afraid. In a new MySQL session:
mysql> show session variables where variable_name = 'tmp_table_size' or variable
_name = 'autocommit';
+----------------+----------+
| Variable_name | Value |
+----------------+----------+
| autocommit | ON |
| tmp_table_size | 13631488 |
+----------------+----------+
2 rows in set (0.00 sec)

mysql> show global variables where variable_name = 'tmp_table_size' or variable_
name = 'autocommit';
+----------------+----------+
| Variable_name | Value |
+----------------+----------+
| autocommit | ON |
| tmp_table_size | 13631488 |
+----------------+----------+
2 rows in set (0.01 sec)
Looks fair, right. So now lets set these two variables in this session:
mysql> set tmp_table_size = 102400;
Query OK, 0 rows affected (0.00 sec)

mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
OK, now let's look at the result, in global and session scope again:
mysql> show session variables where variable_name = 'tmp_table_size' or variable
_name = 'autocommit';
+----------------+--------+
| Variable_name | Value |
+----------------+--------+
| autocommit | OFF |
| tmp_table_size | 102400 |
+----------------+--------+
2 rows in set (0.00 sec)

mysql> show global variables where variable_name = 'tmp_table_size' or variable_
name = 'autocommit';
+----------------+----------+
| Variable_name | Value |
+----------------+----------+
| autocommit | OFF |
| tmp_table_size | 13631488 |
+----------------+----------+
2 rows in set (0.00 sec)

Whoa, this doesn't look right, does it? I change one variable and it affects GLOBAL scope, but not for the other variable. And there is a difference between these two variables, which is that autocommit is really a session only variable! So why in heavens name does it pop up when I do a SHOW GLOBAL VARIABLES? And why is the global value changed when I set the session value? This seems to be how it works for all session only variables?
There might be some sense in this, that I do not understand, so please enlighten me! But if this is the case, then the docs are wrong! Like MySQL manual section 5.1.5 that says this: Several system variables exist only as session variables and then goes on to list these, which are all show as above as both local and global (but always with the same value). The same section also states that Most of them are not displayed by SHOW VARIABLES which isn't true at all, actually, they are ALL displayed by SHOW VARIABLES!

And MySQL manual section 12.5.5.41 says that With the GLOBAL modifier, SHOW VARIABLES displays the values that are used for new connections to MySQL which actually isn't true either (just because I set AUTOCOMMIT to 0, and that is the vale displayed by SHOW GLOBAL VARIABLES, new connection will still have AUTOCOMMIT on).

So, what do you say? Am I just confused? Is the docs wrong, or even right in some awkward way? Or is this a bug? Or? And if you are wondering, the effect on the corresponding INFORMATION_SCHEMA tables is the same...

/Karlsson