When a UFO file is generated by RoboFab’s ufoLib, the <advance> element is omitted when width = 0, which, doesn’t seem to be a good habbit though…
Then, when such a UFO file is opened in Glyphs, a zero-width glyph (without an <advance> element) is displayed as if its width = 600, which is, first, very confusing (although it’s silimiar to the behavior of default width when Glyphs creates a new glyph), and second, this also leads to spacing mistakes if the file is saved, because <advance width='600'> will be generated by Glyphs.
I guess this is a bug instead of an intended behavior.
Glyphs 2.1.1 (791)
OS X 10.10.5 (14F27)
