Shift clicking maps make them disappear.

I was going through my chest for my map to make it larger. I had 12 paper in my inventory at that time. When I shift-clicked the map out of the chest and into my inventory, it automatically assumed it was paper and added it to the stack making it 13. I have not tested this out in other areas or in creative so this might be a specific one. Otherwise, this is it. Thanks!
-Llama_lord