Nope, server change. (We went from 4.0.17 to 5.0.45.) From http://dev.mysql.com/doc/refman/4.1/en/upgrading-from-4-0.html:

Incompatible change: TIMESTAMP is returned in MySQL 4.1 as a string in 'YYYY-MM-DD HH:MM:SS' format. (See Section 10.3.1.2, “TIMESTAMP Properties as of MySQL 4.1”.)

(The 4.1 to 5.0 upgrade cautions are in http://dev.mysql.com/doc/refman/5.0/en/upgrading-from-4-1.html.)