Normal Open the bandbox popup several times to see the issue. The first time it opened, the bandpopup has the same width as the bandbox. The second time it opened, its width is shortened. This kind of behavior alternates indefinitely.
test.zul
<bandbox hflex="1"> <bandpopup> <hlayout> <label value="Name" hflex="1" /> <space /> <label value="Surname" hflex="1" /> </hlayout> <hlayout> <textbox value="Peter" hflex="1" /> <space /> <textbox value="Parker" hflex="1" /> </hlayout> </bandpopup> </bandbox>