Often, it takes a couple tries for modifications to the trace channel collision response of a collision preset to actually change.
This behavior is consistent on two computers, both running 4.15. DefaultEngine.ini is writable.
Steps to reproduce:
- Create new project
- Open Project Settings>Engine>Collision
- Select a collision preset and click Edit
- Change the collision response for a trace and click accept
- Click edit again, and observe that the response selection did not change (may take multiple tries)
It seems that most of the time two consecutive attempts will retain the setting.