Teenage confusion: when 'in' means 'on'

A commonplace, but nonetheless annoying phenomenon, concerns my two teenaged sons and the dishwasher. When the amount of used crockery left lying around in their bedrooms starts to exceed the stock of clean dishes and plates in the kitchen cupboards, we issue a parental order for the mucky stuff to be taken downstairs and placed 'in' the dishwasher. But this apparently simple instruction is nearly always mistranslated in their computer game and streamed music addled brains, so that 'in' becomes 'on top'.
A small problem to the passing reader, perhaps, but one that is seriously starting to affect my already feeble grasp on sanity.