I am sure that something is wrong with your .mkext (Extensions Cache). It cant be rebuild from Leopard 10.5 !!! KP´s without any reason (no IDE active, no old 10.5 kect installed) after some time mostly have reason in an not really working .mkext and/or loading wrong /Extra Extensions from 10.5.
Try to move all needed extra extension out of /extra into /S/L/E and remove /extra extemsions.mkect also to check if thats the problem. Chamelon ofter has problems to load the right /Extra, if you start from an Leopard parition (is active) and select then to start from 10.6 partition. Also an -v into /Extra/boot.plist would show you , if chameleon laod wrong .plist too (without -v / extra of Leopard(active) ). If you didnt see the verbose booting Snow Leo (/extra .plist has -v at kernel flag) than it load complete false Extra content from 10.5.