steps to reproduce

1. run the attached file, 3411.zul

actual result

There is an extra space between the bottom of the window and the bottom of the page.

Since we specify vflex="1", the window's height should extend to fill the page's height.

expected result

There should be no space between the bottom of the window and the bottom of the page.

debug info

1. t3879.zul is the original user's case
2. resize a browser, the window's height will fill up the page's width

workaround

specify height="100%" on the out-most window.