Redstone Comparator updates on /testforblock automatically without specified block being there

For some reason, whenever I try using comparators to track down success for /testforblock, it works in a different way and it annoys me. First, I want the comparator to TRACK down the specified block in /testforblock <x> <y> <z> <TILENAME>. Second, it wants to automatically turn on to success w/o the specified block being at the location specified.