Mysterious Lines over Glyphs


I'm currently working on a font and I've found an issue which baffles me, shown here: [[]]. As you can see there are these out of place lines over the "u" and "y" glyphs, and they're not the only affected glyphs. The issue crops up in Photoshop when the font is displayed at small sizes or has anti-aliasing off. What's weird is that the lines don't actually exist on the vectors, FontLab renders them appropriately and there's nothing suspect on the offending glyphs which sets them appart from the others that render properly.

Help would be much appreciated.