1. Use the following zul.
win1 is an invisible window whose "left" attribute is set.
win2 is a visible window whose "left" attribute is set.
2. click "show" button.
a reproducing case in fiddle:
"win1" is 50px left to screen's left border.
"win1" is at screen's left border.
You can set "top", and you'll also get the same result. The invisible window's position doesn't change.
If we set "left" and "top" attributes at them same time, the invisible window location will be as expected.