Why did it change into 2 programs???

Ok here is the problem.
I was editing some tags and the window looked like the one on your home page.

Here is what I was doing it.
I was editing some tag that had a generic "Various Artist" to the true artist name.
I would cut the name from the song title then past it into the artist name.
Then I would hit the "Save" icon.

Well I look up at the screen and the panel on the left side is gone only the panel with all of the columns is on the screen.

I tried going to view and selecting the "tag Panel" but it would not go back into the main window it acted like it was a seperate program.

What did I do to do this and what should I do the next time to correct the problem.

Is this what you mean: Attachment 416 not found.

If so, simply double click on the title bar of the child window or drag it to the left hand side of MP3Tag.

What did I accidently click on to make it look this way??

Either double-clicked the grip of the panel or moved it off the left side.