Digital Signature placement: Dragging area by 1/2in steps

I'm using Acrobat X Pro and have a problem adding signature to my documents. Usually I'm using the command "Digitally sign document" to insert my signature in a specific area of my documents. Since today, the command still work but now I can't drag my signature's area to a precise rectangular like before (it needs to be contained in an existing rectangular in my document) but now when I drag it seems to go by steps of 1/2in x 1/2in. By doing so I can still insert my signature but it will either exceed or be smaller than the area it needs to fit because I cannot drag it precisely to my document's rectangular... Hope my explanations are clear enough!