This is probably a font cache problem. Read this please:
http://www.glyphsapp.com/tutorials/eliminating-font-cache-problems
You should use the Adobe Fonts folder instead:
http://www.glyphsapp.com/tutorials/testing-your-fonts-in-adobe-apps
Also, keep in mind that lazy symbol glyphs are incompatible with TrueType-based fonts, i.e., TTF and most webfont formats.