steps to reproduce

1. load the attached zul
2. reduce the width of the left-top panel which contains a calendar by 10px

current result

all panels shrink their width, so it produces a blank area on the right-hand side of the portal layout

expected result

when shrinking a panel's width, there should not be a blank area in a portallayout. It looks like a bug.

expected specification

• Under a portallayout's vertical orientation, when resizing a panel's width, only panels in the adjacent column resize their width accordingly.
  e.g. if there are 3 columns in a portallayout, if you enlarge the left-most panel 100 px, then panels in the middle column reduce their width for 100px.