Setting host from a field within a data input file

I have added this to $local/props.conf and $local/transforms.conf, respectively:

# props.conf
# CUSTOM

[snmp-trap]
pulldown_type = true 
maxDist = 3
TIME_FORMAT = %b %d %H:%M:%S
MAX_TIMESTAMP_LOOKAHEAD = 32
TRANSFORMS = snmp-trap-host
REPORT-snmp-trap = snmp-trap-extractions
SHOULD_LINEMERGE = False

# transform.conf 
# CUSTOM

[snmp-trap-host]
DEST_KEY = MetaData:Host
REGEX = (?:[0-9]{1,3}\.){3}[0-9]{1,3}
FORMAT = host::$1

[snmp-trap-extractions]
REGEX = ^(\d{4}-\d{2}-\d{2})\s(\d{2}:\d{2}:\d{2})\s([a-zA-Z]*)
FORMAT = trap_oid::$3

And some sample output from the file I'm using as a data input is:

2011-10-03 10:05:40 ciscoConfigManEvent Normal "Status Events" 10.219.49.51 - Notification of a configuration management event as commandLine running commandSource

I've deleted the data input and re-added it, I've also restarted splunk.

So from the example above, I'm trying to set the host to 10.219.49.51. Problem is that it doesn't seem to be using the host from the regex in props.conf to populate the host field when I realtime search for matches since the restart.

Can anyone see anything that I've missed?