OK! I found the reference to Xrecurse_legacy4 -- I'd missed it earlier because I was hunting in C (.c/.h) source, not in Assembler Language source (.s/.S) code.
I found it in /usr/src/sys/arch/i386/i386/vector.s -- interrupt handling for i386.
Your traceback refers to APM -- which is the likely culprit for the panic -- though the specific reason for the problem is unclear without the panic message. But knowing what we know, you can disable APM, as bsdfan666 first suggested we discussed earlier, and see if your problem goes away.
To disable it permanently, use:
# config -ef /bsd
and enter "disable apm" and "quit" as bsdfan666 had shown above. Then reboot.