Changes have been made in Git (master):

commit 42c8c979783461de9136732a14c686d91118f544
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Thu Dec 27 12:28:25 2012 -0500

     This seems to be required for some RDBMS when migrating.

     When migrating from a previous column definition, and no default is
     given for the current definiation, the previous definition's default
     is used. Must override that with a valid default for the current
     column type.

     Bug: 11877

  .../15_horde_activesync_integerimapuidfield.php    |    3 ++-
  1 files changed, 2 insertions(+), 1 deletions(-)

http://git.horde.org/horde-git/-/commit/42c8c979783461de9136732a14c686d91118f544

Another user reports the same problem on the horde mailing list:
http://lists.horde.org/archives/horde/Week-of-Mon-20121224/045976.html

Going to call this not a bug. WIll reopen if others report similar problems.

Hi!
following output:
mysql> DESCRIBE horde_activesync_mailmap;
+---------------+--------------+------+-----+---------+-------+
| Field         | Type         | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+-------+
| message_uid   | varchar(255) | NO   | MUL |         |       |
| sync_key      | varchar(255) | NO   |     |         |       |
| sync_devid    | varchar(255) | NO   | MUL |         |       |
| sync_folderid | varchar(255) | NO   | MUL |         |       |
| sync_user     | varchar(255) | YES  |     | NULL    |       |
| sync_read     | tinyint(1)   | YES  |     | NULL    |       |
| sync_deleted  | tinyint(1)   | YES  |     | NULL    |       |
| sync_flagged  | tinyint(1)   | YES  |     | NULL    |       |
+---------------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

The problem ist the default ''
when i manually enter
  ALTER TABLE `horde_activesync_mailmap` CHANGE `message_uid` 
`message_uid` int(11);

it works and the new table looks likemysql> DESCRIBE horde_activesync_mailmap;
+---------------+--------------+------+-----+---------+-------+
| Field         | Type         | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+-------+
| message_uid   | int(11)      | YES  | MUL | NULL    |       |
| sync_key      | varchar(255) | NO   |     |         |       |
| sync_devid    | varchar(255) | NO   | MUL |         |       |
| sync_folderid | varchar(255) | NO   | MUL |         |       |
| sync_user     | varchar(255) | YES  |     | NULL    |       |
| sync_read     | tinyint(1)   | YES  |     | NULL    |       |
| sync_deleted  | tinyint(1)   | YES  |     | NULL    |       |
| sync_flagged  | tinyint(1)   | YES  |     | NULL    |       |
+---------------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)


Maybe the problem is a rather old MySQL Version 5.0.45, InnoDB storage 
for this table.

I can't reproduce this. The migration works fine here on MySQL. Can 
you try the following on the MySQL command line and post the results?

DESCRIBE horde_activesync_mailmap;

When upgrading to ActiveSync 2.0.8 or higher the change in the db 
schema leads to the following error in the horde logs when using a 
MySQL Backend

ERR: HORDE [horde] SQL QUERY FAILED: SQLSTATE[42000]: Syntax error or 
access violation: 1067 Invalid default value for 'message_uid'
         ALTER TABLE `horde_activesync_mailmap` CHANGE `message_uid`
           `message_uid` int(11) DEFAULT '' [pid 9525 on line 815 of 
"/usr/share/php/Horde/Db/Adapter/Base.php"]

Best regards,
Alex