Apply this patch that:
{F154534}
1. sets the water rise time to 0 seconds in `extinct_volcano_triggers.js` and a big height increase to make it easily noticeable whther the waterheight is correct or not
2. shows whether it recomputes the graphical data upon deserialization
Then
3. Start hosting a game on extinct volcano. Notice the water level rose immediately. Pause the game.
4. Join as a late observer in a second window and check the waterrendering for height and completeness.
Notice that without the fix applied, the water is not only rendered at the wrong height, but some areas of the map also display it incorrectly:
{F154533,width=1024}
Notice that the result meets the expectation if the patch has been applied.
Read the debug warnings and notice that the recomputation is called if and only if the simulation has changed the waterheight.