What I expected to happen?

When changing the gamemode property, new players would join with that gamemode.

What actually happens?

Players join with the gamemode set at world generation regardless of changes to server.properties afterwards and in contradiction to the gamemode displayed in the console.

Steps to reproduce

1. Create a new BDS Server with default server.properties file
2. Start the server, wait for it to finish initial start, and stop the server gracefully
3. Change the gamemode value to creative
4. Start the BDS instance again
5. Connect with a Minecraft client and note that your gamemode is survival despite the default level being changed to creative.