Boot panic on macbook alluminium

Hi guys! In my boot freebsd install, i have panic:

pci0: <ACPI PCI bus> on pcib0
Memory modified after free 0xc5b026a0(12) val=c0dedead _at_ 0xc5b026a
panic: Most recently used by (null)

cpuid = 0
KDB: enter: panic
[Thread pid 0 tid 100000]
Stopped at kdb_enter+0x3a: movl $0,kdb_why

I can use ddb because the macbook keyboard is usb device,
so i think that before the panic, the kernel doesn't load the
usb keyboard driver.

Thank you,
cheers

Andrea