Inappropriate font substitution

[gagern]

Today I noticed that in applications using the DejaVu Sans Mono font, the aleph symbol U+2135 will be replaced by an incorrect symbol which lookes like a V with a horizontal part at the bottom, and a horizontal line both above and below it. See this screenshot for details. gucharmap indicates that the font actually used apparently is “Mathematica5”. Opening that in fontforge, I find the symbol inquestion at code point 00c0. Although that code point is usually associated with À, in this case it is used for a glyph called “LogicalXnor”. There are two other symbols, “Xnor2” and “Xnor3” in the two subsequent slots, which end up as replacements for U+2111 and U+211C visible in my screenshot as well.

All of this sounds like a bug in some software, or some font, or some configuration, but I don't know which, and where to report it. How can I tell?

Packages on my system which might be relevant to this include:

• media-fonts/dejavu-2.33
  
• media-fonts/mathematica-fonts-7.0
  
• media-libs/fontconfig-2.10.93
  
• gnome-extra/gucharmap-3.8.2
  
• kde-base/kde-meta-4.11.0