With the attribute "modified_subnode" of a node, the timestamp value is modified only if I add or modified subnodes but not when I delete a subnode.

Steps to reproduce

I use in a PHP extension the subtree function of eZContentObjectTreeNode class with this filter:

array( 'ClassFilterType' => 'include', 
          'ClassFilterArray' => [a list of class], 
          'AttributeFilter' => array( 'or', 
                                                  array( 'modified', '>', [a timestamp] ),                
                                                  array( 'modified_subnode', '>', [a timestamp] ) 
                                        ), 
          'Limitation' => array() 
 ); 

If with this filter I can get content when I add or modified subnodes, I can't get content when I delete a subnodes.
Maybe a cache depending on modified_subtree is the problem origin and a cache cleared should resolve the problem.