In the test case there will be an extra height at the bottom of the Grid.
Test case:
<zk>
<div height="30px" style="border: 1px solid green">The height in this Div will affect the height error on the inner Grid.</div>
<tabbox hflex="min" vflex="min">
<tabs>
<tab label="Tab One" />
</tabs>
<tabpanels hflex="min" vflex="min">
<tabpanel hflex="min" vflex="min">
<grid hflex="min" vflex="min">
<columns>
<column hflex="min" />
</columns>
<rows>
<row>
<label value="Top East" />
</row>
</rows>
</grid>
</tabpanel>
</tabpanels>
</tabbox>
</zk>
Bug fixed since 2011/07/08