Well I still can't figure out how it decides to choose another shape in addition to the desired shape when I select the desired shape's layer–however I have found a solution!
Select the layer in the Layer panel, select the Rectangle Tool (U), then CMD click on the shape on the canvas. BAM. The W/H properties are listed only for the desired shape, and I can manipulate them properly.
Way to go me! =)
Thanks for chiming in you guys.