sysparm_device parameter is used when you would like to change different UI for ex UI15, UI16, Mobile, tablet or printer mode etc on your instance.
Following are valid inputs for this parameter
If sysparm_device has any other value then it goes to UI11/Legacy.
For ex. https://XXXXXXXX.service-now.com/navpage.do?sysparm_device=docs
This is intended behavior as per design.