Index: src/wp-includes/wp-db.php
===================================================================
--- src/wp-includes/wp-db.php	(revision 32248)
+++ src/wp-includes/wp-db.php	(working copy)
@@ -2534,7 +2534,7 @@
 
 		if ( $db_check_string ) {
 			$queries = array();
-			foreach ( $data as $col => $value ) {
+			foreach ( $data as $col => &$value ) {
 				if ( ! empty( $value['db'] ) ) {
 					if ( ! isset( $queries[ $value['charset'] ] ) ) {
 						$queries[ $value['charset'] ] = array();
@@ -2542,6 +2542,7 @@
 
 					// Split the CONVERT() calls by charset, so we can make sure the connection is right
 					$queries[ $value['charset'] ][ $col ] = $this->prepare( "CONVERT( %s USING {$value['charset']} )", $value['value'] );
+					unset( $value['db'] );
 				}
 			}
 
Index: tests/phpunit/tests/db/charset.php
===================================================================
--- tests/phpunit/tests/db/charset.php	(revision 32248)
+++ tests/phpunit/tests/db/charset.php	(working copy)
@@ -59,7 +59,6 @@
 				'charset'  => 'koi8r',
 				'value'    => "\xfdord\xf2ress",
 				'expected' => "\xfdord\xf2ress",
-				'db'       => true
 			),
 			'hebrew' => array(
 				// hebrew needs to be checked in MySQL, too
@@ -66,7 +65,6 @@
 				'charset'  => 'hebrew',
 				'value'    => "\xf9ord\xf7ress",
 				'expected' => "\xf9ord\xf7ress",
-				'db'       => true
 			),
 			'false' => array(
 				// false is a column with no character set (ie, a number column)