Why is SLA reapplied on changes to closed tickets

Why is SLA reapplied on changes to closed tickets

Doing some clean up of old tickets after having changed SLA rules.  Noticing the tickets are showing the new sla response and dueby dates - I would ordinarily not want this to recalculate on closed tickets - does this mean all changes on closed tickets now need to be done through sql scripts rather than the interface to avoid this trigger firing?

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