MySQL upgrade breaks replication

Upgrade from 4.1.x and 5.0.22 to 5.0.42 and going forward (5.0.46, 5.0.48) in CentOS breaks replication. The error log now placed as /var/run/mysqld/mysqld.err instead of into the default datadir and the name is mysqld.err instead of .err, is it a MySQL bug?

mysql> start slave;
ERROR 1201 (HY000): Could not initialize master info structure; more error messages can be found in the MySQL error log

071005 13:06:38 [ERROR] Failed to open the relay log ‘/var/run/mysqld/mysqld-relay-bin.000074’ (relay_log_pos 598368274)
071005 13:06:38 [ERROR] Could not find target log during relay log initialization