Working local MCX breaking months after install

Background: Educational environment, InstaDMG 10.5.8 base image working beautifully on iBook G4's, MCX settings restricting certain System Pref Panes (created using WGM) applied as a pkg immediately after asr restore of base image. Everything has been working great since imaging last summer. Recently two problems have been surfacing: The first, non-admin users are presented with a dialog box request from SystemUI Server for the admin password upon launch. This started happening about 2 months ago. All research says this is likely permissions related. Repairing permissions sometimes fixes this but not always. Simply entering admin password makes it go away permanently. Unsure if this is related to bigger problem below. I wasn't concerned about this but in the last week I've had 3 machines come in with another weird error, users cannot browse standard websites in any browser. Users can browse secure websites just fine. Image does have parental controls turned on for logging purposes. If I turn off parental controls, web usage returns to normal but all my custom MCX settings are immediately wiped, users can access all Pref Panes. If I rerun the pkg the MCX settings are correctly reapplied but the browser behavior returns to restricting port 80 traffic. If I completely wipe the disc and reimage, everything behaves perfectly like it did last summer. I'm above my pay grade on this one… anyone have any thoughts about what may be going on under the hood and what I might be able to do to avoid simply wiping the users drive and starting over? And should just turning off Parental Controls completely wipe my custom MCX settings?