Test defective

Bethany • 31 years of age, very opinionated but thoughtful
Well ladies and gentleman. I had a clear blue plus test this morning and I didn't get a positive (I don't think) I didn't get a negative either. I got a very faint line that intersected diagonally to the horizontal line in the test window. 
It's obvious that it's time to retest with a different unit but I am curious for all my medical friends out there, why does this particular thing happen that way