This already has been a problem in the 80ies when Intel VM86 mode came into use - real mode programs tested the unused bits in the status register and then made

This already has been a problem in the 80ies when Intel VM86 mode came into use - real mode programs tested the unused bits in the status register and then made assumptions about the CPU (as recommended by Intel in the programming manuals). When the program was running inside a VM86 environment (virtual real mode inside of protected mode), the instruction for this triggered an protection fault, and the "hypervisor" filled in the results as if it got executed correctly, potentially confusing programs about which CPU they were running on.