@yiming: I tried a bit more, and we are both correct
If the "condensed" font is *not* explicitly overridden using fonthack, it will indeed use the regular Caecilia font, instead of the condensed one (even if fc-match reports otherwise). I don't know why that is or how to fix it.
However, there is a simple workaround: explicitly assign "DejaVu Serif Condensed" as the condensed font. It looks better than Caecilia anyway
