Why would my Mac Pro with Leopard 10.5.1 reboot when I do a safe boot?

Question

I turn on the computer. It bongs. I hold down the shift key and keep it held down. The gray Mac screen appears and then the spinning wheel indicator appears and runs for a few minutes, then the computer just reboots. The computer boots just fine otherwise. I can also boot into single user mode with no problem.
I don't recall trying this when the computer was running 10.4.x, so I can't be sure it's specific to the computer, but my guess is that it's specific to Leopard.
Anyone else try a safe boot under Leopard and had a similar experience?
other keywords: safe mode, extensions off.

Answer 1

Here's what looks like the last portion of the log just before it reboots itself
Dec 31 16:57:48 localhost kernel[0]: Extension "com.apple.iokit.IOBluetoothFamily" has immediate dependencies on both com.apple.kernel and com.apple.kpi components; us$
Dec 31 16:57:48: --- last message repeated 2 times ---
Dec 31 16:57:48 localhost kernel[0]: E:[AppleUSBBluetoothHCIController][FindInterfaces] mInt0InterruptMaxPacketSize = 16
Dec 31 16:57:52 localhost kernel[0]: can't remove kernel __LINKEDIT segment - in-kernel linker needs it
Dec 31 16:57:52 localhost kextd[9]: in-memory mkext doesn't match on-disk mkext; non-boot kexts won't be loaded
ec 31 16:57:52 localhost configd[13]: InterfaceNamer: No network stack object
Dec 31 16:57:53 Macintosh configd[13]: setting hostname to "Macintosh.local"
Dec 31 16:57:53 Macintosh configd[13]: InterfaceNamer: No network stack object
Dec 31 16:57:53 Macintosh mDNSResponder mDNSResponder-164 (Nov 4 2007 13:23:04)[16]: starting
Dec 31 16:57:54 Macintosh mDNSResponder[16]: SetDomainSecrets: mDNSKeychainGetSecrets failed error 0 CFArrayRef 00000000
Dec 31 16:57:54 Macintosh com.apple.launchd[1] (com.openssh.sshd): Unknown key: SHAuthorizationRight
Dec 31 16:57:55 Macintosh configd[13]: InterfaceNamer: No network stack object
Dec 31 16:58:02: --- last message repeated 8 times ---
Dec 31 16:58:02 Macintosh kextd[9]: writing kernel link data to /var/run/mach.sym
Dec 31 16:58:03 Macintosh kernel[0]: can't remove kernel __LINKEDIT segment - in-kernel linker needs it
Dec 31 16:58:07 Macintosh configd[13]: InterfaceNamer: No network stack object
Dec 31 16:58:08: --- last message repeated 3 times ---
Dec 31 16:58:08 Macintosh com.apple.launchctl.System[2]: kextcache: WARNING: readCaches got mount point after 1 tries