Reading the Wikipedia page on Halt and Catch Fire it seems this issue actually caused a certain set of illegal opcodes to become an "official' HCF instruction (

Reading the Wikipedia page on Halt and Catch Fire it seems this issue actually caused a certain set of illegal opcodes to become an "official' HCF instruction (opcode was DD so it was also known as "Drop Dead") as it was also later used by the engineers for product testing or something.