You interpretation itself is correct, but the issue lies with your firmware. The behavior you are describing is a known UEFI-bug:
For the memory management functions in EFI, an OS is meant to be able to use "memory type" values above 0x80000000 for its own purposes. In the OVMF EFI firmware release "r11337" (for Qemu, etc) there is a bug where the firmware assumes the memory type is within the range of values defined for EFI's own use, and uses the memory type as an array index. The end result is an "array index out of bounds" bug; where the higher memory type values (e.g. perfectly legal values above 0x80000000) cause the 64-bit version of the firmware to crash (page fault), and cause incorrect "attribute" values to be reported by the 32-bit version of the firmware.