In Diablo 2 version 1.11 and 1.11b, there is a bug regarding the socketing of ethereal armors. Ethereal armors are assigned a 50% bonus to their base defense rating when dropped. This is normal. What is not normal is the fact that when sockets are added to an ethereal armor using the Horadric Cube, that ethereal defense bonus is applied again. The result is an armor with an absolutely impossible defense rating. Enhanced defense modifiers are then added to that base defense rating, so the difference in end defense is rather huge.
This bug appeared as a side-effect when the 1.10 ethereal armor upgrade bug was fixed (the bug is described in section 14). In order to fix that bug, a defense bonus of 50% was simply crammed into the ethereal unique armor upgrade formula. Unfortunately that fix also affected the ethereal armor socketing formula, making armors now gain a second defense bonus when socketed.
The use of this bug is very controversial, and that is the reason I havent added this section earlier. The overwhelming number of questions asked about this forced me to make up my mind.
It is not debatable whether this is a "bug" or an "undocumented feature". It is obviously a result of a programming flaw, making it a bug. Ask anyone who has looked at the code, ethereal armors gaining defense when socketed is NOT intentional. Not a chance.
However, the community is split regarding the practical use of this bug. One half argues that since Blizzard hasnt removed the bug, they intend it to stay, and that they need the bugged armors to stay competent when compared to those who do use the bugged armors. The other half considers the use of any ingame bugs to their advantage to be cheating. Personally, I agree with the second group, and suggest that anyone who wants to consider oneself a legitimate gamer to avoid this bug until fixed.