Computers are not pulling packages from their local Package Server but instead are pulling packages from the NS or another Package Server that is not part of their Site. No error messages are received but the following verbose logs might include the following:
The resource is not contained within any sites. Returning the NS codebases only.
The Altiris Profiler code tab for GetPackageInfo includes an entry "ClosestSites" with value of the Sites which returned the Package Servers list it belongs to.
ITMS 8.x
When sites are created, the SMP expects that each IP's subnet in the GetPackageInfo request xml belongs to a Site which it will return a list of Package Servers in that Site. If the IP's subnet(s) or super scopes in the client request are not included in any Site, the SMP returns the closest site based on the IP's subnet and it's relative super scopes. What can happen is that a super scope is included within a Site, which is accordingly picked by the SMP.
Insure than all of your subnets are assigned to Sites and that each site has a valid Package Server.
This behavior is under review by EPM development team and there might be changes in the future releases.