MySQL not updating a row (zero row(s) affected) I cannot figure out why MySQL 5.6.25 will not update an existing row:

SELECT
  lcl_booking.file_number_id,
  lcl_booking.entered_datetime,
  lcl_booking.modified_datetime
FROM lcl_booking
WHERE lcl_booking.file_number_id = 197467;


yields:

file_number_id entered_datetime     modified_datetime
197467         2015-06-26 15:26:44  2015-07-08 10:39:15


Now, I do this:

UPDATE lcl_booking SET
  modified_datetime = "2015-07-21 10:54:04"
WHERE file_number_id = 197467;


returns:

1 queries executed, 1 success, 0 errors, 0 warnings

Query: UPDATE lcl_booking SET modified_datetime = "2015-07-21 10:54:04" WHERE file_number_id = 197467

0 row(s) affected

Execution Time : 0.019 sec
Transfer Time  : 0 sec
Total Time     : 0.019 sec


and....

SELECT
  lcl_booking.file_number_id,
  lcl_booking.entered_datetime,
  lcl_booking.modified_datetime
FROM lcl_booking
WHERE lcl_booking.file_number_id = 197467;


yields:

file_number_id entered_datetime     modified_datetime
197467         2015-06-26 15:26:44  2015-07-08 10:39:15


Here is the table (minus a bunch of columns)

SHOW CREATE TABLE lcl_booking;

CREATE TABLE `lcl_booking` (
  `file_number_id` bigint(20) unsigned NOT NULL,
  `entered_datetime` datetime NOT NULL,
  `modified_datetime` datetime NOT NULL,
PRIMARY KEY (`file_number_id`),
KEY `lcl_booking_fk1` (`file_number_id`),
CONSTRAINT `lcl_booking_fk1` FOREIGN KEY (`file_number_id`) REFERENCES `lcl_file_number` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT='LCL Booking Header';


Anyone have any ideas?
It was an undocumented trigger that was causing the problem.