Color difference between drawRect and drawString

Wow, this is an odd one. Thanks for letting me know!

You can do this in the emulator:

require("Font8x16").add(Graphics);
var grf = Graphics.createArrayBuffer(8,16,4,{interleavex:true});
grf.setBgColor(0);
grf.clear();
grf.setFont("8x16",1);
grf.setColor(2);
grf.drawString("X",0,0);
grf.drawRect(7,0,8,8);

for (var y=0;y<16;y++){
  var s = "";
  for (var x=0;x<8;x++)
    s += grf.getPixel(x,y);
  print(s);
}

I think this is related to custom fonts. If you use a built-in or vector you should be ok?