Defective holder?

I got my first blinking smiley face (using the advanced digital ovulation test) on November 26th, and have had a blinking smiley face everyday since then (7 days). I ran out of tests so I bought a new set today. I used the new test stick holder and got an empty circle. I started to doubt that the old holder was working, so I tested again in the same day (only a few hours later) using the old holder but new sticks and got a blinking smiley face again. I'm concerned, not only that I have wasted a month of trying to get pregnant with a defective holder (especially since my cycles are sooo long and irregular to waste any time is very annoying), but also because ovulation tests are SUPER expensive.

I know it says to not start using a new holder in the middle of your cycle-that you might get different results, by why would it matter? Isn't the test either suppose to detect the hormone or not?? Why would it need to 'know' whether you are at the beginning of a cycle or in the middle? That seems fishy to me.