Strange from a perceptible angle, sure, but in the context of a software anomaly, not strange at all: repopulating the attribute for the policy isn't all that different from "blow away the plist and that'll fix it".
Was the policy previously working under a prior state? Did some change break it (e.g. an update on a client, on the JSS, ...)? Or was it created fresh and it didn't work with your initial display message setting?
