While traveling in the overworld towards a goblin dark fortress, my framerate suddenly started chugging and my memory usage shot up to 13 GB for the DF .exe file, and then I got ambushed by a pack of dingoes. This save is in the ambush, dingos to the left.

Closing the game fully and reloading the save reproduces the memory leak. Escaping from the dingos and moving away from that overmap area or returning to the main menu causes memory usage to return to normal.