If Windows 10 Edition-Player joins a singleplayer world on Switch, the Switch-Player dies instantly

Hi guys,

sorry for my bad English, but i have to write in this language because more people can help me to solve this problem.

On my Nintendo Switch I logged myself in with my Microsoft Account. My friend has a Windows 10 Minecraft version and he wanted to join my world. I started a singleplayer world on my Switch and because we are friends in the XBOX Live System, he found my world in his list. While I was loading my world, he joined into my world. He spawned first while i was still loading into the world and waiting for me to spawn. My friend told me that around him were items like a diamond pickaxe. And after a long time, my Switch loaded myself into the world. But I was instanty dead. After a respawn I was back in my house and all my Items from my inventory were gone. All Items layed next to my friends spawnarea. And thats every time a new friend enters my personal world on my Nintendo Switch. I don't know why.