Have I just found a bug in GTK+ ComboBox?

[Anton Ermolenko <aner fastmail com>]

Hello!

Context: https://bitbucket.org/p2t2p/gtkcombodemo/src/19be8dfe788c1aec1
a5384eb107facaa38e121ff/main.js?at=master&fileviewer=file-view-default



TL;DR

GTK+ renders ComboBox popup off-screen if the item is too low in the
list.
Help needed:
 * Please confirm if it is a bug or if there is such a bug.
 * How do I figure out the version of GTK+ installed?
 * What environment data GTK+ team needs to confirm if this is a bug?



Long story

I'm writing a small utility which uses GTK+ ComboBox widget.
I have a pretty long list of 2 cells in that ComboBox.

First cell is a GIcon
Second cell is text (gchar* I think).

I'm showing a list of apps installed on a machine in that ComboBox.

I think I'm doing something wrong or I've discovered a bug:

Whenever I select an item in this ComboBox popup which is located
at certain "distance" from the top in the list of all items, this
ComboBox stops showing the popup. Whenever I click on the ComboBox
it highlights itself but the popup is invisible. It reacts to arrow
keys, though. If I press arrow key and then if I press enter the 
selection changes. I believe it renders the popup off-screen.

That happens only if I pick an item at certain distance from the top in
the list.
If I pick an item which is closer to the top it works fine.
Also it seems that this distance depends on the window position on the 
screen - the lower window on the screen, the longer the "failure"
distance.

I've prepared a short demo which reproduces the behaviour
on _my_ machine: https://bitbucket.org/p2t2p/gtkcombodemo/src/19be8dfe7
88c1aec1a5384eb107facaa38e121ff/main.js?at=master&fileviewer=file-view-
default


Thank you!