Comment 11 for bug 1467588

Confirmed for me too. It happens in several terminal issued commands involving GUI.
The last of those command was Zenity dialog.
"GtkDialog mapped without a transient parent. This is discouraged." appeared after each Zenity step (2): one for choose a direcctory to copy, and one for choose a directory where copy previously selected files.

My OS environment:
----------------------- Actual system description ---------------------
kernel name is: Linux
kernel-release is: 4.4.0-36-generic
kernel version is: #55-Ubuntu SMP Thu Aug 11 18:00:59 UTC 2016
machine hardware is: i686
processor type is: i686
h/w platform is: i686
**************** OS specs *******************
operating system is: GNU/Linux
desktop env. is: xubuntu - XDG_CURRENT_DESKTOP=XFCE
Distributor ID: xenial
Description: Ubuntu
Release: Ubuntu 16.04.1 LTS
Codename: 16.04