Comment # 14 on bug 1161823 from Michael Chang

This new zstd feature introduced by 2.04 only got disabled for i386-pc because
it broke some running setup if installing grub to partition, ie btrfs
bootloader area or mbr gap aligned to cylinder boundary with which some dual
boot system with Micorsof Windows may suffer. Such regression is not allowed in
migration path so it was disabled until good solution can be found then we can
enable this "new" feature. That being said if you want compression for btrfs on
i386-pc you need to use zlib or lzo.