What exactly triggers EVENT_POI_UPDATED?

[SnowmanDK]

From what I can see, it triggers at odd times, which makes addons utilize extra cpu time for no reason.

A good example I have been made aware off, is if you run between the wayshrine and the guild traders in Belkarth.
It triggers around the bridge every time, but there is NO changes in the values it returns, and I already know all POI's in that zone. It doesn't even change between zone/submap.
Does it have to do with distance to POI's?