I wonder that too. When I pulled the stick part out of the digital part, it had 2 bold blue lines, when even the test I took earlier in the morning (a dipstick one, supposed to detect 20 miU) was still really faint. Weird!
We don't have those here! We only have the ditigial - + ones. My test yesterday (10 DPO) was pretty dark, with a drug store brand test and today's, an FRER was really faint. I'm staying positive though.