Image size on different layers linked?

Hi, I'm having a frustrating problem trying to remove myself from a photo.  I found the only way to remove my shadow as well is to cut out the parts of the image that I want, then place that over another image of the same background without me in it.  So I have 1 layer mask with the desired subject in one image and another layer with a different image of the same background.  The problem is the 2 images appear to be different sizes (thus, the background details don't match up), and when I try to re-size one image (on its own layer) photoshop also re-sizes the other image on the other layer.  I have done nothing to link these layers or images together.  I have tried re-importing the background image because that seems to be the only time I can fine-tune the size... however Ps won't allow me to see my layer mask at the same time as I am re-sizing the new image.  As soon as I click on anything other than the new image (to re-order layers) I am no longer able to drag the new image by its corner.  I'm sure there's something stupid that I'm missing here, can anyone help?