I didn't recall seeing this mentioned or asked - how tight are the tires when mounting? Do you always mount tires starting at the same point on the rim? Is is possible that a tight bead is pushing the rim tape over and partially exposing the nipple holes? And when the pressure is removed (by deflation) that the rim tape returns to it's intended position, hiding the cause?

I realize that this isn't what rim tape is supposed to do, but with the lack of another explanation (so far) you have to look at outliers, no?