The policy is being changed for the system in some way. You will need to identify why ePO is giving the system the incorrect policy.
Check for duplicate machines: From the ePO system tree, while at "My Organization", select the preset for "This group and all subgroups" and perform a quick find for the system name.
Check the explicit policy assignment for the system: Select the system and click Actions | Directory Management | View Assigned Policies.
Check that the last communication time shown in ePO matches that of the client system.
Verify that the solution found in KB52949 has been applied.
If using tagging and a PAR to apply the policy, verify the system is tagged.
If using system tree based policy assignment, verify the system didn't move to a different location in the system tree.