10.5.6 build and single-user mode

So I build a 10.5.6 InstaDMG image on a Late-08 MacBook Pro 15". (The only package update is the 10.5.6 combo update, and it's built off of a 10.5.4 Retail DVD dmg). I then apply the resulting image to the same machine. I reboot that machine into single user mode, and it freezes at the "Loading System\Library\Extensions.mkext..." part. Anyone know what's going on here? Perhaps, is it anything to do with the "Updating Boot Caches" message that sometimes pops up after installing system updates? I can get the same behavior with my entire package, including all the Apple and custom PKGs. Which is what prompted me to try with a basic 10.5.6 image. Very odd. Thanks, --joe