Probably related to the post from yesterday ("How the 8086 processor's microcode engine works" (righto.com) https://news.ycombinator.com/item?id=33845941 https:

Probably related to the post from yesterday ("How the 8086 processor's microcode engine works" (righto.com) https://news.ycombinator.com/item?id=33845941 https://news.ycombinator.com/item?id=33845941), which explains why "[...] the processor ignores certain bits when decoding instructions."