3ds Max always saves a backup file when merging file into it.
Disabling the Auto-Backup function does not solve the issue.
To stop the saving behaviour of 3ds Max at opening/merging a scene file:
Open the Scene Converter at: Rendering > Scene Converter
Disable the function Backup Original Files:
BUT, some max versions just do not save this settings, so you have
to, always for every scene, over and over, check this settings.
This small startup scripts save the time and nervs!
Just put it into