For me it looks like that defoma generates wrong substitutes in the Fontmap (/var/lib/defoma/gs.d/dirs/fonts/Fontmap), like Arial-BoldItalic for Helvetica-BoldItalic and I have no idea from where it gets these substitute names. Or it does not put any lines telling which font file Arial-BoldItalic is (It is probably /usr/share/fonts/truetype/msttcorefonts/arialbi.ttf or /usr/share/fonts/truetype/msttcorefonts/Arial_Bold_Italic.ttf of the msttcorefonts package which is installed on my system.
For me it looks like that defoma generates wrong substitutes in the Fontmap (/var/lib/ defoma/ gs.d/dirs/ fonts/Fontmap) , like Arial-BoldItalic for Helvetica- BoldItalic and I have no idea from where it gets these substitute names. Or it does not put any lines telling which font file Arial-BoldItalic is (It is probably /usr/share/ fonts/truetype/ msttcorefonts/ arialbi. ttf or /usr/share/ fonts/truetype/ msttcorefonts/ Arial_Bold_ Italic. ttf of the msttcorefonts package which is installed on my system.