We recently made some changes to our infrastructure and now I can't keep MySQL replication running. The slave complains of a corrupt binlog and resetting it doesn't help. I keep seeing entries like this in my master log:

BINLOG '
WFxKTRNJAAAAPwAAAKY/YwAAABsAAAAAAAEACHdlYmVkaTMwAA1QYXJ0bmVyQ29uZmlnAAQICA8P
BC0AYwAA
WFxKTRhJAAAAXAAAAAJAYwAAABsAAAAAAAEABP//8BoSAAAAAAAAggMAAAAAAAAJUEFDS0NPVU5U
Azc3MfAaEgAAAAAAAIIDAAAAAAAACVBBQ0tDT1VOVAM3NzI=
'/*!*/;

In the slave log, this just comes across as "Unknown Event" and the replication fails at that position.

Here is my my.cnf for the master:

[mysqld]
datadir=/data/mysql-data
socket=/tmp/mysql.sock
user=mysql
log-error=/var/log/mysqld.log
binlog-do-db    = db1
binlog-do-db    = db2
binlog-do-db    = db3
binlog-do-db    = db4
binlog_format   = 'MIXED'
log-bin = /data/mysql-binlogs/mysql-bin.log
server-id=73
report-host=thisserver.mydomain.com
thread_cache_size = 30
key_buffer_size = 700M
myisam_sort_buffer_size = 300M
table_cache = 256
sort_buffer_size = 4M
read_buffer_size = 1M
innodb_data_home_dir            = /data/mysql-data/
innodb_data_file_path           = InnoDB:100M:autoextend
set-variable                    = innodb_buffer_pool_size=500M
set-variable                    = innodb_additional_mem_pool_size=10M
set-variable                    = max_connections=500
innodb_log_group_home_dir       = /data/mysql-data
set-variable                    = innodb_log_file_size=20M
set-variable                    = innodb_log_buffer_size=8M
innodb_flush_log_at_trx_commit  = 1

Does anybody know what might be causing the gibberish in my master binlogs?