It sounds like we're re-imaging a machine(s), and if that's the case, then we would see the policy history get flushed. By default, the JSS would view this machine as a "new" client, and remove the information about what policies have run. So, if it meets the scoping criteria you're using, the clients would re-run any appropriate policies.
If you're not wanting this event to happen, there is a command that can be run to turn this off in the database management framework, and if you would need that, feel free to contact support@jamfsoftware.com and your Account Manager can provide that for you.
Hope that helps clear up this question!
Drew - JAMF Software