<?xml version="1.0" encoding="UTF-8"?>
<window id="root" border="normal" >
When you shorten the size of the left tabbox by drag and drop the splitter, the size of the left tabbox should calculate as you expected.

<hbox width="600px" sizedByContent="false">

<tabbox id="tabbox" style="width:100%">

<tabs>
<tab label="Tab 1" />
<tab label="Tab 2" />
</tabs>

<tabpanels>

<tabpanel>
<tree id="ncstree" vflex="true" >

<treechildren>
<treeitem label="group 1" open="false" />
<treeitem label="group 2" open="false" />
<treeitem label="group 3" open="false" />
<treeitem label="group 4" open="false" />
<treeitem label="group 5" open="false" />
<treeitem label="group 6" open="false" />
<treeitem label="group 7" open="false" />
<treeitem label="group 8" open="false" />
<treeitem label="group 9" open="false" />
<treeitem label="group 10" open="false" />
</treechildren>

</tree>
</tabpanel>

<tabpanel>
</tabpanel>

</tabpanels>

</tabbox>

<splitter id="split"/>

<window id="contents" width="100%" height="100%" border="none" >
</window>


</hbox>
</window>