DHXWindows error positioning - scrolling error

Hi!
I wish to display a popup window on a scrolled page.

When initializing the DHTMLXWindows in onLoad (code below), the scroll bar on the page disappears.
dhxWins = new dhtmlXWindows();
It seems like the initialization triggers the class dhxwins_vp_[dhtmlx-skin-name] - removing the scroll.
I have added a style on the body so you can scroll down to the button - for demo purposes!

Also, the window does not display in the right place.
When scrolling down to the button the window opens at the top of the page.
I have tried “dhxWins.window(windowId).centerOnScreen()” to no avail.
See example below:
snippet.dhtmlx.com/147838330

Q1. How should DHTMLXWindows be initialized so that scroll is preserved?
Q2. How should the window be opened to center on the visible part of the screen when scrolled down to the button?

Kind regards.
/K

Please check the updated snippet. snippet.dhtmlx.com/e85a60952
By moving scroll to a separate DIV you can solve both issue ( blocked scroll and incorrect position )