auto update of image widths

Hi,

I’m having issues with Dreamweaver which automatically alters the width values of my image when I change/swap an image.

The width value is set to 100% (width=100%) as the image is held in a responsive div container. When I come to alter the image (double click on the image in design view) or alter the “Src” in the properties tab the new image is automatically changed from the 100% value to an absolute value (400).

../image/example1.jpg" alt="image 1" width="100%" />

changes to

../image/example2.jpg" alt="image 2" width="400" />

I can alter the width manually, but it is inconvenient and easy to miss.

How do I stop this automatic feature in Dreamweaver?

Thanks for reading my question