Evap lines on cheap tests

So I took an 88 cent Walmart First Signal test this morning. I waited the 4 minutes it says and it was negative. I threw the test out immediately. Later I saw it in the trash and it had a faint PINK positive line. So I took another test and watched it while it was working. A faint pink line shows up around 5 to 6 mins. This is under the 10 minute mark where it says the test results will be invalid but over the 4 minutes the instructions said it would work by. What are your opinions???