I uploaded a font family that included a number of variations on a single font (for example, "Regular", "Bold", "Light". "Distressed"). I'm able to use the standard version of this font just fine, but when I try to select other variations of it from the drop-down menu just to the right of the font-selection menu, it displays all the different variations but will not allow me to use them. When I try selecting one, it just defaults back to the standard "Regular" font option.
Could you see whether you can use those variations in Mac apps like Pages or Keynote? If it works there, it's probably a bug with Pixelmator, in which case we'd love to hear from you at support@pixelmator.com.