Images included:
http://s1060.photobucket.com/user/ItzMIilooooXDD/media/y_zpsfa415749.png.html
http://s1060.photobucket.com/user/ItzMIilooooXDD/media/y2_zpsf5c208f0.png.html

It could be that while they are the same pair of glasses, WeeWorld has two identical items with the same appearance/price but with different item IDs. This would cause them to be treated separately, despite appearing to be identical.

Another possibility is that it is simply a bug-- if it is causing you trouble, for whatever reason, you may report the bug to WeeWorld.