Sailed to Ashen Shores for a treasure hunt (thanks, map).
When I first got into the region, I took one damage proc every two rounds.
However, after landing in treasure location and then getting back into ship, I started taking two damage procs every two rounds, and it kept going even as I went through quads, or even tried to go under deck and then back above it.
Only leaving the region entirely stopped the procs. For testing reasons, sailed right back into the region after leaving it - started taking single damage proc per two rounds again.
I noticed I got "Immune to Fire" for a moment after getting on ship, also. Is that just safety net once getting back on ship in the region or something else?
Extract from log, search for "pirate chest" to see the split before and after
