Ooh well you can get evvaporation lines after kit dries giving false positives , thats why the instructions tell you only to read the result within a given timeline, I remember getting this tho on my really week test results , was ages before I got a proper good bfp on a test, and then when I looked back at my first BFN tests, which I had kept (nice I know!) , they had lines on them too, which was strange!!
How old is the test you are looking at with a line?