Why is rpm trigger %triggerpostun not used when installing via yum?

Issue

One of our rpm need to do stuff when kernel is installed/remove ie: (un)link some modules in /lib/modules/<kernelversion>/extra/
To achieve that, we're using some rpm triggers (%triggerin, %triggerun and %triggerpostun)
If the rpm is installed via the rpm command, everything works fine. But if our rpm is in a repository and is installed via yum, the %triggerpostun is not launched.

Using RPM

# rpm -e target
triggerun source 1-1 1 0
triggerpostun source 1-1 1 0
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Using YUM

# yum remove target
=============================================================================================================================================================================
 Package                                  Arch                                     Version                                  Repository                                   Size
==============================================================================================================================================================================
Removing:
 target                                   noarch                                   2-0                                      installed                                   0.0  

Transaction Summary
==============================================================================================================================================================================
Remove        1 Package

Installed size: 0  
Is this ok [y/N]: y
Downloading Packages:
Running Transaction Check
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
  Erasing    : target-2-0.noarch                                                                                                                                          1/1 
triggerun source 1-1 1 0
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
MISSING OUTPUT
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Removed:
  target.noarch 0:2-0                                                                                                                                                         

Complete!