Setting the Weight to Thin, seems to put the weightClass at 250 (this is the number shown next to the drop down in Glyphs 2), in the Help it states that Thin is “100” — is this a bug? When I set a weight to Thin and Extralight: Extralight shows up before Thin in Adobe menus, probably because Thin and Extralight are in the same weightClass?
You can set your own weightClass with the weightClass parameter. This is explained here:
http://www.glyphsapp.com/tutorials/multiple-masters-part-3-setting-up-instances
There is a “bug” in some older Microsoft renderers. It would force bolden all fonts that have a weightclass lower than 250. So I tried to avoid this.