Modal scrolling does not work when dropdown is open

Please see in jsfiddle: link

With dropdown menu open, modal scroll does not work, it gets frozen.

What am I doing wrong?

Follow the code below:

.modal-body {
    max-height: calc(110vh - 210px);
    overflow-y: auto;
}

Here is the image:

The red line does not work, while the yellow line is open.

Tested browsers:

It does not work: Google Chorme and Opera.

It works: Firefox, Microsoft Edge, Internet Explorer