We have a complex knockout page where we have a Bootstrap Modal that opens up and then we open a simple BootstrapDialog modal on top of it.   When the BootstrapDialog modal is closed the initial Modal will no longer scroll with the page.   The solution that worked for me was as simple as this.  If this solution doesn’t work there were a few more complex solutions on the referenced page.

.modal { overflow: auto !important; }

Code Credit goes to jofftiquez on Github