Oops! This happens as a result of clicking too many times. It can also happen because Envio remembers where you last opened the screen-- so if you had it open on a different monitor or behind the main screen when you last shut down, it may just be opening up where you last looked at it.
If you click on a line item three times (accidentally) instead of two, it will open the new window, but then the third click will ask Envio to bring the original page into focus and you land back on the main page.
It looks as if the page is opening behind, when it is actually opening in front, correctly, after the second click. Then at the third click, the page is then told to "get back there" so that main page is the focus. (Click four times and you get two of the same new windows open)