The bug is caused by this test case zktest/test2/F50-3000873.zul

In this case, you should see the "bottom east" and "bottom west" under the bottom of the tabbox. Otherwise, it is a bug.

For example,

<window id="tabView" title="Case 2" closable="true" hflex="min" width="500px">
<borderlayout hflex="min" vflex="min">
<north hflex="min" vflex="min">

<tabbox hflex="min" vflex="min">
<tabs>
<tab label="Tab One"/>
<tab id="tab2" label="Tab Two"/>
</tabs>

<tabpanels hflex="min" vflex="min">
<tabpanel hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min"/>
<column hflex="min"/>
</columns>
<rows>
<row>
<label value="Top East"/>
<textbox />
</row>
</rows>
</grid>

</tabpanel>
<tabpanel hflex="min" vflex="min">
<borderlayout hflex="min" vflex="min">
<west hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min"/>
<column hflex="min"/>
</columns>
<rows>
<row>
<label value="File:"/>
<textbox width="98%"/>
</row>
<row>
<label value="Type:"/>
<hbox>
<listbox rows="1" mold="select">
<listitem label="Java Files,(*.java)"/>
<listitem label="All Files,(.)"/>
</listbox>
<button label="Browse..."/>
</hbox>
</row>
<row>
<label value="Options:"/>
<textbox rows="3" hflex="min" vflex="min"/>
</row>
</rows>
</grid>
</west>
<east hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min"/>
<column hflex="min"/>
</columns>
<rows>
<row>
<label value="Top East"/>
<textbox />
</row>
</rows>
</grid>

</east>
</borderlayout>

</tabpanel>
</tabpanels>
</tabbox>
</north>
<center hflex="min" vflex="min">
<borderlayout hflex="min" vflex="min">
<west hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min"/>
<column hflex="min"/>
</columns>
<rows>
<row>
<label value="Bottom West"/>
<textbox />
</row>
</rows>
</grid>
</west>
<east hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min"/>
<column hflex="min"/>
</columns>
<rows>
<row>
<label value="Bottom East"/>
<textbox />
</row>
</rows>
</grid>
</east>
</borderlayout>
</center>
</borderlayout>
</window>