Cast iron cookware may start to rust
Cast iron pots and pans can rust if you put them in a dishwasher. The rust marks can spread onto your cutlery or the tub of the dishwasher. If you put your tin opener in for instance, the little cog that cuts the can open is made from iron and will rust quite easily.
Try and avoid washing cast iron pots and pans in your dishwasher.
Always disconnect your appliance from the mains before you start examining it!