After importing an Altium board into KiCad, DRC ran on KiCad's defaults, 0.2 mm clearance and 0.5 mm to the edge. The author's 10 mil track and clearance, via sizes, mask rules and room-scoped rules were never read, so the board passed or failed against rules nobody wrote. The current workaround is a per-board fix_pcb.py script.