Some fonts don't include bold and italic font styles. Currently, text formatted with such fonts and with applied bold or italic formatting is exported without the italic or bold effect. Instead, the default typeface can be exported, and additional transformation could be applied to the letters itself - e.g. skew transform for the italic.
Note: It seems that the GlyphTypeface for such fonts is using a non-italic (non-bold) font file and has StyleSimulations property set to ItalicSimulation (BoldSimulation) which is used in order to render the glyphs italic.