The problem is the Mac version of the Pango library that MonoDevelop uses to render fonts does not currently support font backups for missing glyphs. Typically, if Japanese characters are not available in the font, rendering should return to the glyph from the default Japanese font.
MonoDevelop 2.4 Beta 1 supports custom font settings for output pads, so as a workaround you can set Okasa as a font for output pads.
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