MySQL - Cannot add or update a child row: a foreign key constraint fails

This seems to be a common error, but for the life of me I can't figure this out.

I have a set of InnoDB user tables in MySQL that are tied together via foreign key; the parent user table, and a set of child tables that store email addresses, actions, etc. These are all tied to the parent user table by a foreign key, uid, with all of the parent and child keys being int(10).

All of the child tables have a uid value with a foreign key constraint pointing to user.uid, and set to ON DELETE CASCADE and ON UPDATE CASCADE.

When I delete a user from user, all of the child constrained entries are removed. However, when I attempt to update a user.uid value, it results in the following error, rather than cascading the uid change to the child tables:

#1452 - Cannot add or update a child row: a foreign key constraint fails (`accounts`.`user_email`, CONSTRAINT `user_email_ibfk_2` FOREIGN KEY (`uid`) REFERENCES `user` (`uid`) ON DELETE CASCADE ON UPDATE CASCADE)

I have a feeling I must be missing something obvious here. Removing the key constraint with user_email and attempting to update the value in user results in the same error but for the next alphabetical user child table, so I don't believe it is a table-specific error.

EDIT:

Adding in the results from SHOW ENGINE INNODB STATUS:

------------------------
LATEST FOREIGN KEY ERROR
------------------------
121018 22:35:41 Transaction:
TRANSACTION 0 5564387, ACTIVE 0 sec, process no 1619, OS thread id 2957499248 updating or deleting, thread declared inside InnoDB 499
mysql tables in use 1, locked 1
17 lock struct(s), heap size 2496, 9 row lock(s), undo log entries 2
MySQL thread id 3435659, query id 24068634 localhost root Updating
UPDATE `accounts`.`user` SET `uid` = '1' WHERE `user`.`uid` = 306
Foreign key constraint fails for table `accounts`.`user_email`:
,
  CONSTRAINT `user_email_ibfk_2` FOREIGN KEY (`uid`) REFERENCES `user` (`uid`) ON DELETE CASCADE ON UPDATE CASCADE
Trying to add in child table, in index `uid` tuple:
DATA TUPLE: 2 fields;
...
A bunch of hex code

But in parent table `accounts`.`user`, in index `PRIMARY`,
the closest match we can find is record:
...
A bunch of hex code

Solution

On an unrelated task, I recently brought up our MySQL database in MySQL Workbench, and when viewing the table relations for the above tables, I noticed 'duplicate' and/or spurious relations that I had somehow missed before (they weren't showing up in PHPMyAdmin FWIW). Removing these extra relations cleared up the issue immediately.