Odd network problem with InstaDMG-generated image

Since September, we have had an odd problem in our labs where a user will sit down to a machine which is already logged in (using a local, standard account with some MCX controls), will open (or switch to) a web browser and not be able to surf the net. Cached pages may load, but new ones will not. I can access all other networking functions perfectly, including file sharing and ARD remote control. The fix: logout then log back in to the account. The problem does return eventually, but logging out and back in (or using Fast User Switching to login to the admin account, open a web browser — which then works — logout of the admin account and log back in to the standard user account) is the immediate fix. This problem happens only periodically, but enough to be a PITA. It does not seem to be model-specific (most of our Macs have had the problem at one time or another). The images being deployed are both a pure InstaDMG image and an image that was generated by InstaDMG then manually tweaked and cloned. They have been deployed both by DeployStudio (1.6.6) and Disk Utility. We zapped the PRAM on all the machines yesterday just in case that might fix it. No idea if it has worked (too soon to tell). Anyone else having this problem? Anyone have any suggestions about what files in the master might need to be killed? (I'm suspecting a rogue package, probably one that I created using Composer or PackageMaker.) [u]Tech specs:[/u] Mac OS X 10.5.8 (10.5.0 disk image with combo update package) InstaDMG 1.5rc1 Two local accounts: one admin, one standard (with MCX settings added after the fact) No network accounts Images built on a Mac Pro (early 2008) Deployed to Power Mac G5 (all generations), Mac Pro (2006) and Mac mini (late 2009) machines.