Why do gradients seem to be a separate entity from a shape?

I'm currently trying to draw a shape and have its color as a gradient, using the fill tool. However, when I move the shape around to where I need it to be placed, it would seem as if the gradient is a separate object, as the shape "decolorates" as I move it about the canvas. How can I  make the gradient "stick" to the shape? Is it even possible?

Thank you.