The bug

When a world is already open in another instance of the game, a red warning text is shown, there is no play button and you cannot click on it to focus it:

However, it is possible to select the world with the keyboard:

• Using up and down arrow keys
• Using tab key in case world is first one in list

This should not be possible, because it enables all buttons and pressing some of them causes errors.

Reproduction steps

1. Open the game twice
2. In one instance open a world
3. In the second instance open the world selection
   It should show the warning text for the world which is already open
4. Use the tab key or select another world, then press the up or down arrow keys
   It is possible to select the world which is already open
5. Press "Edit"
   An error occurs