Panic on otherwise stable machine

[John Klos <john%ziaspace.com@localhost>]

This is a dual processor Sun Fire v245 with 16 gigs. After about two or so 
months of uptime while compiling pkgsrc packages non-stop, I got a panic:

trap type 0x68: cpu 0, pc=7f40bc npc=7f40c0 pstate=0x820092<,PEF,IE>
Skipping crash dump on recursive panic
panic: +fast data access MMU miss
cpu0: Begin traceback...
cpu0: End traceback...
cpu1: shutting down
cpu0: rebooting

Since work is interrupted, I'm taking this time to update to the latest 
netbsd-8. It was running netbsd-8 from the beginning of June.

Any ideas about what happened here?

John