Its just impossible to Pause the Game. I had something to do, but didnt wanted to close the game, so I just returned to the Switch Home Menu and put it into Standby mode. When I returned after 10 Minutes, I woke up my switch and continued to the Game. First I saw a short loading screen then there were no Block Textures Visible, only the sky and entitys. I saw the Daylightcyle, but 10 times faster then usual. It seems that it kept running while the switch was in standby and tried to load everything that happened while I was not there. After It loaded everything, I just saw a death scene which shows, that a zombie killed me. All my items already despawned and are now forever gone. 
Even if you press the + Button on your Controller, you see the game menu, but the game still keeps running. I dont want to exit my Map every single time I have to go away for a short time..

Steps to reproduce (Game isn't paused when I press the Menu Button)
1. Enter a world
2. Place some entitys, jump off a cliff, just do something so there is something moving on the screen
3. press the Menu Button  ( + )
4. You can see, that the game menu is opened, but the Game is still running (the entitys are moving/you are still falling etc. 

Steps to reproduce (Game keeps running when I go to standby mode)
1. Join in a Survival Map
2. turn the difficulty to easy, normal or hard.
3. Just stand somewhere
4. Return to the Switch Home menu 
5. turn on the standby mode
6. wait a bit, for example 20 minutes, in that time, something should kill you
7. if you return, you will likely see a death screen