Evert Pot was seeing some weird issues with his MySQL BOOL usage via PDO when he upgraded to one of the latest versions (5.6). Thankfully, he's shared his solution to the problem as well as the symptoms he was seeing when it was causing problems.

I recently updated my workstation to run MySQL 5.6.13. It didn't take very long for things to start breaking, and since I couldn't find any other information about this on the web, I figured this may be useful to someone else. The main error that started popping up was: "Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 1366 Incorrect integer value: '' for column 'my_bool' at row 1' in test.php" This exception happens under the condition that you use PDO, prepared statements and booleans.

He includes a small sample script to reproduce the issue and points out the issue - the default casting of prepared values to strings in prepared statements with PDO bound parameters. He shows two "relatively easy solutions" to the problem - either using integers instead of the true/false PHP boolean or specifying a type with the bindValue call.