Changes in MySQL 5.1.26 (30 June 2008)
Functionality added or changed:

Important Change: Incompatible Change: The FEDERATED storage engine is now disabled by default in binary distributions. The engine is still available and can be enabled by starting the server with the --federated option. (Bug#37069)

Bugs fixed:

Replication: Performing an insert on a table having an AUTO_INCREMENT column and an INSERT trigger that was being replicated from a master running MySQL 5.0 or any version of MySQL 5.1 up to and including MySQL 5.1.11 to a slave running MySQL 5.1.12 or later caused the replication slave to crash. (Bug#36443)

See also Bug#33029

Row-based replication broke for utf8 CHAR columns longer than 85 characters. (Bug#37426)

NOT IN subqueries that selected MIN() or MAX() values but produced an empty result could cause a server crash. (Bug#37004)

ha_innodb.so was incorrectly installed in the lib/mysql directory rather than in lib/mysql/plugin. (Bug#36434)

An empty bit-string literal (b'') caused a server crash. Now the value is parsed as an empty bit value (which is treated as an empty string in string context or 0 in numeric context). (Bug#35658)

The code for detecting a byte order mark (BOM) caused mysql to crash for empty input. (Bug#35480)

The mysql client incorrectly parsed statements containing the word “delimiter” in mid-statement. (Bug#33812)