Ahem, read carefully. Holding down Alt while typing on the numpad is a different input method from Alt-X. With the Alt-numpad method, you hold down the Alt key while typing in your numbers IN DECIMAL (and according to a mapping that varies from Unicode for a significant number of characters), then release after the last digit, so the span of digits is well defined. With the Alt-X method, you type in HEXADECIMAL digits (0-9,A-F/a-f) first, THEN type Alt-X, and it takes the digits you just typed and converts them. Typing 30(Alt-X) should give you a zero character, but if you typed in, say, ediface(Alt-X), Windows has four possible look-behind choices: e, ce, ace, face. It should choose the last (the longest string of uninterrupted hex digits), producing edi followed by some wonky character.

Problem is, suppose you wanted "glacé". If you typed in glace, then the hex digits for é with no leading zeros, then typed Alt-X, you'd get something like gl (or gla) followed by some strange character (not the accented e) because a and c are also hexadecimal digits, and the look-behind span isn't delimited. However, I think the maximum number of hex characters that the Alt-X method will consider is four, so padding with leading zeros should remove any ambiguities (if you don't mind the extra typing). This method wasn't well thought out--and it only works with Word and some other Microsoft programs, not with every application (as Alt-numpad should).

So it's your understanding that's flawed, and next time watch the tone in which you "correct" someone, leaving you hauteur out of it.