Bumping up the discussion from Glyphs 2.3 Collected Issues:
The fsType custom parameter is still confusing people 
The dialog says “no set” but the table says “Installable” for the zero value.
This is still an issue with the 2.4 beta!
There is another problem too, originally reported on the Font Bakery Github issue tracker.
When a Python macro sets font.customParameter['fsType'] = 0, Glyphs will export the font with 1 instead!
However, if the user manually changes this field by hand, it will be exported as 0.
This sucks! 
To get the same result as from the UI you need to set this:
Font.customParameters['fsType'] = []
But I fixed your case with setting the number directly.
Thank you Georg!!
In Improving the output · Issue #1071 · googlefonts/fontbakery · GitHub @alexeiva said,
Add a new custom Parameter like this:
Produces this result
New ParameterThe Workaround is to set
fstypeto any other value, i.e.editable, and then set back toun set.
Then it will work properly:
This sucks!
