Prevent the browser scrollbar from disappearing in Colorbox

Hello : )

I recently bought a HTML template from MotoCMS and I´m quite happy with it. There is only an annoying behavior in the Colorbox plugin, which comes with the template.

Each time I open up a picture with Colorbox the browser scrollbar disappears, to center the picture in the middle of the display.
This causes the content of the background page to jump to the right – and back to the left, when you close the picture.

This is very annoying and I would like to prevent the browser scrollbar from disappearing in Colorbox. But I have no idea where
to search for the relevant code …. in “colorbox.css” or in “jquery.colorbox.js” – I have no idea.

Can anybody help?

Many thanks in front and best regards

chris