positive and negative result from same sample

Hello,

Today it was first day of testing in this cycle. I used the ovulation test (4 more fertile days) and got solid smiley face - peek fertility. I then used another test from 2 best days I had from my previous cycle (same holder, obviously unused strips), and it came back negative. I used same urine sample. Given tests state to be 99% accurate, this seems very odd. Could you shed some light on this?