fonttools: [T1Lib] T1Font.saveAs() broken?

After doing:

t1 = T1Font('font.pfb')
t1.parse()
t1.saveAs('font-out.pfb', 'PFB')

and trying to open the resulting pfb file in fontforge I get an error from fontforge:

Didn’t understand "/… " in blended font defn

This happens for every .pfb font I’ve tried (the original files are opened in fontforge with no problems at all).

Using the latest pip3 install of fontTools