There was no bug that needed to be fixed. This change has caused a
bug. Though some individuals may consider this underline change an
enhancement, it's also technically a BUG since it changes default
behavior. The change could still go in as long as it doesn't change
the way underlined text has displayed for years.
I looked into best practices for underlining. Bringhurst barely mentions
it (I checked both the first and the second edition), but briefly notes,
under underscore "To clear descenders, a repositioned version of the
character is required" (page 286).
Dowding on the other hand is more forthcoming. Having first warned
against underlining in principle: "Underlining as a method of
emphasizing a word or phrase in a displayed setting is a crude relic of
Victorian typography. Emphasis can, & should, be achieved in other ways"
(page 77) he then gives advice on how to do it: "If one is compelled to
underline then the underlining must be properly done. The rule must be
close to 'the line' or feet of the letters. Where there is a descender,
the rule should be set on each side of it. When a descender comes at
the beginning or end of a word in lower-case that has to be underlined,
set the rule fairly close to the feet of the non-descending letters
only." (page 78)
There follows a figure, where underlining on the word "Begin" avoids the
descender of the "g", and also where underlining on the word "many"
avoids the descender of the "y" (and is also cut off at an angle, to
match the slope of the descender). My edition was published in 1995; the
first edition was 1954. The claim of "30 years of underline behavior"
can clearly be put to rest by 64 years of typographic commentary.
Bringhurst, Robert "The Elements of Typographic Style". Second edition,
Dowding, Geoffrey "Finer Points in the spacing & arrangement of Type".
Third revised edition, 1995.
Technical Director @ W3C
W3C Strategy Team, Core Web Design
W3C Architecture & Technology Team, Core Web & Media