Wrapping Blocks within Stacks

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I've been trying to set a block wrapper which works fine EXCEPT with stacks:
<?php
            $leftColumn = new Area('Left Column');
            $leftColumn->setBlockWrapperStart('<div class="blockWrapper shadowBox">');
            $leftColumn->setBlockWrapperEnd('<div class="clear"><!-- --></div></div>');
            $leftColumn->display($c);
?>

When a stack is encountered the wrapper is put around the entire stack of blocks instead of around each block. This seems like a bug?

Please can anyone help me resolve this problem?