Positive or Evap lines?

I took two tests yesterday morning- both Walmart brand. I immediately saw faint lines appear and disappear as the dye faded through. I threw them in a drawer a little disappointed, and went to work. I came home last night and found the original faint lines present on both tests, with a straight dark line on the side. What the heck? I had a faint positive on Sunday, now this. What does that mean?