When the -o option is used to the dhcp_probe command, all the output
to the file seems to be garbled.

# dhcp_probe -f eth0 -o /dev/stdout
note:   starting, version 1.3.0
warn:   received unexpected response on interface eth0 from BootP/DHCP
server with IP source 10.70.18.1 (ether src 0:21:d8:8:e:bf).
²¡Hv#xGO[r
VVަ!EH─ÿö
F
F9CD4f
F9
F D
FަcSc5ÿÿÿ:F;   :3
6
warn:   received unexpected response on interface eth0 from BootP/DHCP
server with IP source 10.70.18.1 (ether src 0:21:d8:8:e:bf).
F Dÿ#xGO&s
VVަ!EH─ÿ
F
FCD4h)
F
F B
FަcSc5ÿÿÿ:F;   :3
6
^C^C^C


System Information:

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 6.0.3 (squeeze)
Release:        6.0.3
Codename:       squeeze

# uname -a
Linux asfrouter 2.6.32-5-686-bigmem #1 SMP Mon Oct 3 05:03:32 UTC 2011
i686 GNU/Linux

# dpkg -l | grep -i dhcp
ii  dhcp-probe                         1.3.0-5
network DHCP or BootP server discover
ii  isc-dhcp-client                    4.1.1-P1-15+squeeze3
ISC DHCP client
ii  isc-dhcp-common                    4.1.1-P1-15+squeeze3
common files used by all the isc-dhcp* packages
ii  isc-dhcp-relay                     4.1.1-P1-15+squeeze3
ISC DHCP relay daemon
ii  isc-dhcp-server                    4.1.1-P1-15+squeeze3
ISC DHCP server for automatic IP address assignment

Control: tags -1 + moreinfo

This looks like two same-structured similar packets in the pcap output.
You haven't posted the output itself so it's unclear to me how you'd
know it's mangled?