Im traying to fill the preferred family and preferred subfamily in 7.5, all good there, but when exporting some font, wont save that info. And other fonts will export perfectly.
I dont know what may be the problem. 
I found that I got the results that I wanted by ignoring the “Extended” settings, and just entered the Family and Subfamily on the Identification Tab.
it looks like it has to be different things so it to stay filled. If not, it will erase that part.
In some cases the OpenType specification does not allow to specify these naming values; e.g. when they are equal to the regular naming fields.
If you press the Help button you will see an explanation:
Preferred Family; For historical reasons, font families have contained a maximum of four styles, but font designers may group more than four fonts to a single family. The Preferred Family allows font designers to include the preferred family grouping which contains more than four fonts. This ID is only present if it is different from Font Family.
Preferred Subfamily; Allows font designers to include the preferred subfamily grouping that is more descriptive than Font Subfamily. This ID is only present if it is different from Font Subfamily and must be unique for the the Preferred Family.