When we switched to FOP 0.95 and re-ran PFMReader on our .pfm files, the line spacing suddenly became distorted on lines that contained fo:inline tags that used a different font-family.
It turned out that the font metrics produced by FOP 0.95 have an inverted sign for the descender value. When inverting it again (i.e. remove the minus sign in the font metrics xml), all was well again.
It seems that this is due to changes to PFMFile in r56078 for bug#43089. Our fix was to invert the sign in PFMReader on producing the metrics file, since the sign inversion in PFMFile seems to be needed.