Why do I get a second window when playing MKV

[Animedude5555]

I a MKV video with MKVtoolnix featuring 2 separate video streams. The intent was to play it and be able to select one or the other stream to play at a time using VLC's video stream selection menu. But it didn't work. Instead, I have stream 1 playing in the main window, and a popup window that plays stream 2, and the control to select the video stream has NO EFFECT at all on what is playing. What is going on, and how do I fix it?

[Animedude5555]

What's this? Several people have viewed this but nobody knows how to fix it? This is ridiculous.