Opening a certain number of windows closes already open windows

[Andrew Hayzen]

I'm not sure this is specifically the ubuntu-ui-toolkit, but if I use a Label vs Text seems to affect the number of windows I can open so thought I'd check here first.

What happened:
1) Branch the demo-app [0]
2) Launch the app
3) Notice a window appears with a number
4) Click anywhere in the window to launch another window with an incremented number
5) Keep clicking on the first window, generating a large number of windows
6) Notice at a certain number as the window is spawning all the other windows close.

For me this happens at different times depending on the environment/app, if I change the Label inside the Window to Text it happens later, or if I switch from the LXD/LXC based SDK to running $ qmlscene directly on the host this also increases the number of windows I can generate.

------|-Label-|-Text-|
LXD---|---61--|--81--|
Host--|--125--|--143-|

What I expected to happen:
For me to be able to keep generating a number of windows without other windows being closed.

Note: When I found this issue in a more complex app, the lowest limit was 14 not 61 windows, so the complexity of the app may affect this.

0 - https://code.launchpad.net/~ahayzen/+junk/multi-window-issue

Environment:
Unity7, 16.04, with stable overlay PPA.

$ apt-cache policy qtdeclarative5-ubuntu-ui-toolkit-plugin ubuntu-sdk-ide
qtdeclarative5-ubuntu-ui-toolkit-plugin:
  Installed: 1.3.2085+16.04.20160916
  Candidate: 1.3.2085+16.04.20160916
  Version table:
 *** 1.3.2085+16.04.20160916 100
        100 /var/lib/dpkg/status
     1.3.2085+16.04.20160915 500
        500 http://ppa.launchpad.net/ci-train-ppa-service/stable-phone-overlay/ubuntu xenial/main amd64 Packages
     1.3.1918+16.04.20160404-0ubuntu1 500
        500 http://gb.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
ubuntu-sdk-ide:
  Installed: 4.1.0~161+201609151241~ubuntu16.04.1
  Candidate: 4.1.0~161+201609151241~ubuntu16.04.1
  Version table:
 *** 4.1.0~161+201609151241~ubuntu16.04.1 500
        500 http://ppa.launchpad.net/ubuntu-sdk-team/ppa/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

$ lsb_release -rd
Description: Ubuntu 16.04.1 LTS
Release: 16.04

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09

[Andrew Hayzen (ahayzen)]

Note this doesn't seem to be a memory pressure as the qmlscene process is around 40MB.