Unlike the other invisible spacing and mark glyphs, zerowidthjoiner contains a displaced question mark glyph. zerowidthjoiner should be set to appear without the question mark block like similar letters.
The sequence [a, zerowidthjoiner, b, c] will currently look like what the image below shows in the edit mode.
Can you double-check that the glyph name is zerowidthjoiner and its Unicode is 200D? There should not be any question mark box.
It is the same as the default setting.
Do you use a custom preview font? Because I don’t see any placeholder, either in the font view nor the edit view. What version of MacOS do you have?
I am not aware of any function in Glyphs that will let one change what font is used as preview for glyphs that haven’t been drawn yet. If it’s this you are referring to by custom preview font, then that should not have been used and everything should be the same as the default setting.
I am currently using a mac with High Sierra version 10.13.6. The replacement for this old pc won’t arrive for a few more weeks though.
The issue seems to still be present in my setup.
I can confirm that this is only a problem in 10.13 and probably earlier. I’ll disable placeholders for all “Separator” glyphs.
Thanks, that sounds reasonable.