To reproduce:
(open system manager, or equivalent)
1. Open map
2. Click on a kingdom, switch between kingdoms, or zoom back out from a kingdom to the world map
Each time you carry out one of the above steps the memory usage increases.
Some weird things:
This happens on the first opening of the map, and for the next few times (less and less (or maybe less likely to?) each time). Then this seems to stop.
8 GB of ram
No mods