emerging font-alias-1.0.3 installs /usr/share/fonts/75dpi/fonts.alias ; /usr/share/fonts/misc/fonts.alias and possibly a couple of others, which maps names to iso8859-1 fonts which might not be existing on the system since media-fonts/font-adobe-75dpi-1.0.3 and media-fonts/font-misc-misc-1.1.2 actually install iso10646-1 fonts.
As a consequence of this, applications that refer to fonts via aliases (such as media-sound/baudline) will fail. (See Bug 426654 )
I understand from the mkfontdir's manual page that fonts.alias files are to be edited by hand, however, since the font-alias package is pulled in as a dependency by the font packages, I believe it would be just great if they were just in accordance.
I just fixed some bugs that were caused by iso8859-1 not being installed if USE=-nls:
Author: Matt Turner <email@example.com>
Date: Sat May 26 12:52:46 2018 -0700
xorg-2.eclass: Always install iso8859-1
I think this bug might be another case of that. I don't see either of the packages you mention installing iso10646-1, so I'm kind of confused.
Going to make as RESOLVED/TEST-REQUEST. Please let me know.