We don't have PAW so this information may be incorrect, but my understanding is the review date is only reset by clicking the 'Reviewed it' button on the My Reviews tab in the dashboard (or manually editing the review date).

The review date is not updated each time the map is re-published; it is x frequency since the date the first version was published. (There can be many reasons a map is republished without having been reviewed eg transfer ownership, which means it's not always appropriate to update the review date when maps are republished.)

Thanks @Noala - that sounds reasonable. I'll check this out.