What a lovely variation of the old theme "The PDO SQL parser breaks your SQL". This is not a MySQL bug. This is not a driver bug. 

You have hit two PDO bugs!

However, you bug report is close to Bogus. Please pay more attention on your bug report. Well prepared bugs, including reproducible code examples, have a higher chance to be taken care of then bug reports like yours.

--- Bug 1 -- Type conversion

Your example is bogus. PDO does not promise not to change the variable type of a bound variable. PHP is dynamic and loosely typed. Its very "PHPish" from PDO not to take too much care about it.

However, if you care about types you should read the manually carefully and try all options on types which the API provides:

 bool PDOStatement::bindParam  ( mixed $parameter  , mixed &$variable  [, int $data_type  [, int $length  [, mixed $driver_options  ]]] )


You can give PDO a type hint when binding parameters. Make use of it:

$id = 1;
$mybool = false;
$stmt = $db->prepare('INSERT INTO test(id, mybool) VALUES (?, ?)');
$stmt->bindParam(1, $id);
$stmt->bindParam(2, $mybool, PDO::PARAM_BOOL);

If you do so, your variable will at least not change its type before you call execute(). If you omit this additional parameter your variable will be converted into a string by the call to bindParam().

However, at lastest the type of your variable $mybool will change from boolean to string due to a bug in ext/pdo/pdo_sql_parser.c upon execution of the statement. The file pdo_sql_parser.c comes from the PDO core module. It has nothing to do with MySQL.

The "bug" (PDO does not promise not to change the type of your bound parameters!) is around line 480. PDO recognizes that it got a boolean value and converts it into an PHP integer (long). It does this within a switch-case construct and falls through to the default handling. The default handling will convert the variable again from integer to string. 

You can check this yourself and do a quick hack of the parser using a "convert_back_to_boolean" flag.

And why do you try to bind a PHP boolean variable to an integer SQL column? Wouldn't it be more appropriate to use a PHP integer variable for a SQL integer column? PDO has not automatic PHP to SQL type mapping. 


--- Bug 2 --- PDOs SQL parser

PDOs SQL parser is very, very basic. It takes your INSERT statement and replaces all placeholders with string values!

For example, INSERT INTO test(id, mybool) VALUES (?, ?) will be converted by the INSERT INTO test(id, mybool) VALUES ('<somevalue>', '<somevalue>'). Of course MySQL will bail at you, if you send such a SQL statement! 

Search the bug archive for more examples of PDO generating invalid SQL.



--- What can you do? ---

- use ext/mysqli and be happy

 (nothing)
 (nothing)
 (nothing)

 - fix PDO
 - use MySQLs native prepared statements and keep your fingers off from named parameters and the PDO SQL parser

An *important* addition to 
--- Bug 2 --- PDOs SQL parser :

It is your task to teach the SQL parser that a value shall not be interpreted as a string. Make use of the PDO::PARAM_<type> constants! PDO can't know what you intend to do. PDO will always fall back to the safe default of strings and quote even integers unless you tell PDO not to do so!

What uwe said..