Index: wp-admin/includes/file.php
===================================================================
--- wp-admin/includes/file.php	(revision 19625)
+++ wp-admin/includes/file.php	(working copy)
@@ -1065,7 +1065,12 @@
 
 <?php
 foreach ( (array) $extra_fields as $field ) {
-	if ( isset( $_POST[ $field ] ) )
+	if ( is_array( $_POST[ $field ] ) ) {
+		foreach ( $_POST[ $field ] as $array_map )
+			echo '<input type="hidden" name="' . esc_attr( $field ) . '[]" value="' . esc_attr( stripslashes_deep( $array_map ) ) . '" />';
+
+	}
+	elseif ( isset( $_POST[ $field ] ) )
 		echo '<input type="hidden" name="' . esc_attr( $field ) . '" value="' . esc_attr( stripslashes( $_POST[ $field ] ) ) . '" />';
 }
 submit_button( __( 'Proceed' ), 'button', 'upgrade' );