2015/2016 scaling JS control add-ins

Hi all,

Scaling JS add-ins is giving me a headache. Imagine a page with only one field, which is the add-on.
I'll best explain with some screenshots.

First, this is how the add-in looks in any browser (this screenshot is even rendered in IE8 mode)
Note the borders I've set to make everything clear. The body has a dashed border, the content a solid border.
If the content exceeds the div, a y-scrollbar is shown as expected.


Now the same add-in in NAV. RequestedHeight:300, RequestedWidth:300, VerticalStretch:false, HorizontalStretch:false.
Note that the bottom and right borders aren't showing. No x or y-scrollbars even though the content far exceeds the div.


Now the same add-in in NAV. RequestedHeight:300, RequestedWidth:300, VerticalStretch:true, HorizontalStretch:true.
Note that the bottom and right borders aren't showing. No y-scrollbar even though the content far exceeds the div.


Any ideas on how to make NAV behave like any browser would?
I just want the add-in to take up all the available space and respect the viewport.
(PS. of course, in the web client it works fine )