What happened was, I have two named items called "Keycard," and when I used the tesfor command, one item turned into the other.

Steps to Replicate:
1) Get an iron hoe and a blaze rod and name them "Keycard."
2) Place down a command block and enter the command,

testfor @p {SelectedItemSlot:0,Inventory:[{Slot:0b,tag:{display:{Name:"Keycard"}}}]}

and attach a button to it.
3) Drag one of the "Keycard" items into the first slot and click the button.
4) Scroll away from the item and click the button again to reset it.
5) Drag the second "Keycard" Item into the first slot and click the button again
6) The second item will turn into the first item, still named "Keycard".