Copy/Paste using rectangular marquee tool reduces the pasted image size

When I copy the top part of a selected image using the rectangular marquee tool (2592px x 72px) and then paste it the pasted image remains the same size of 2592px x 72px like below:

The pasted image remains the same size as the copy:

Now if I select the bottom part of the image (layer) and copy this:

When I paste this the image size reduces from 2592px x 72px to 2567px x 72px:

Is there a way of copy/pasting without the pasted image being smaller than the copied image and remaining the same size? I have tried two computers with two Photoshops and they are the same on both. 

Thanks in advance