Back when Intel introduced the 80286, they didn't quite document everything right away. Errata were needed. Then the 80386 changed things. And then someone convinced them to add just one more feature at the last minute, which didn't get documented properly again.
The History of a Security Hole takes a look at the problems introduced by the I/O Permission Bitmap (IOPB) in the 80286, and how fallout from the implementation caused a security hole in all versions of OpenBSD up to 6.3 and NetBSD up to 4.4.
Conclusion? This programming thing is hard.
(Score: 3, Interesting) by DavePolaschek on Thursday September 06 2018, @05:52PM
If you followed Intel's initial 386 PRM (from 1986), the padding byte wasn't documented at all. The April 1986 datasheet documented it correctly, but differently. The 1989 386 SX PRM finally documented it all correctly, three years late. And then a slew of technical books came out in the early 90s (also covered in TFA) which got it wrong in various ways.
Fun!