I simply removed the position: fixed style from the _modal.scss file and it seems to work fine for me. I still have the background and it works as expected.
// Modal background
.modal-backdrop {
/* commented out position: fixed - bug fix */
//position: fixed;
top: 0;
right: 0;
bottom: 0;
left: 0;
z-index: $zindex-modal-backdrop;
background-color: $modal-backdrop-bg;
// Fade for backdrop
&.fade {
opacity: 0;
}
Kudos to Rick Strahl for the guidance in "Bootstrap Modal Dialog showing under Modal Background".