I know you probably used FMU to do the test, but when was the last time before that, that you went to the loo? If you went in the early hours of the morning, then technically that would have been your FMU, and not what you used to test with, so the result would look feinter, kwim? Or it could be possible that the test was faulty, even though it was the same as the others you've used. There could be tons of different reasons why the test this morning wasn't as dark as the others.