Please describe the problem:
In the GtkTextView help we can see that the position of the scrollbars is controlled by GtkAdjustment (I'm interested in vertical position), and "page_size" field represents the size of the visible scrollable area, while "upper" represents the most far point (which is the bottom of the text view if I understood).

Now see this piece of code:
the equivalent thing happens in C but I report it in C# because it is smaller.

Steps to reproduce:
[CODE SNIP]
1: textview1.SetBorderWindowSize(TextWindowType.Right, 30);
2: send = Gtk.Image.NewFromIconName("gtk-ok", IconSize.Menu);
3: textview1.AddChildInWindow(send, TextWindowType.Right, 0, 10);

4: scrolledwindow1.Vadjustment.Changed += delegate {
   4.1: Gtk.Adjustment adj = scrolledwindow1.Vadjustment;
   4.2: int value = (int) (adj.Upper - 16);
   4.3: textview1.MoveChild(send, 0, value);
};
[CODE SNIP END]

This is what it does:
1: sets a border in the text view right area
2: create a widget (an image from stock)
3: add the widget into the border, in position x=0 y=10 (bottom left of the border)

4: register to the changed signal, fired when the adjustment changes size (resized or lines added)
4.1: get the adjustment
4.2: calculate where to put the widget

Actual results:
I want it always in the bottom left of the border, because I've put it in the y=upper-16, which is the most far point minus the image height.

It correctly works well when resizing the text area, but not when I scroll

Expected results:
I would like that it works also when I scroll (actually when I scroll the image vanishes or is half displayed, I don't understand why

Does this happen every time?
yes

Other information: