Composite characters or Japanese input gets sometimes sent to the wrong terminal window

At times (I have not found the trigger to reproduce it at will), one terminal window out of many will refuse to receive complex input sequences (such as the French composite accented character "ê" (which is typed with "^ + e" on a french keyboard), or IBus/Anthy Japanese input), and only these characters will be redirected to another terminal window.

This means that for two terminals, typing in terminal 1 : "Verbe être" results in this :
Terminal 1 : "Verbe tre"
Terminal 2 : "ê"

When this happens, the following workarounds work to put things in order :
- close the affected terminal window
- spawn a new one and close it

I am not sure whether this is an IBus problem, or a Gnome Terminal problem at its core.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: gnome-terminal 3.16.2-1ubuntu4
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: GNOME-Flashback:Unity
Date: Mon Oct 31 01:51:06 2016
InstallationDate: Installed on 2010-01-30 (2465 days ago)
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027.1)
SourcePackage: gnome-terminal
UpgradeStatus: Upgraded to wily on 2016-04-16 (197 days ago)