Warning after Page is pruned

After a Page which has a component with a mixin with an embedded mixin, has been pruned we get this warning because mixinBeforeOrderer and/or mixinAfterOrderer already contain the embedded mixin.

[WARN] GridCell Could not add object with duplicate id 'org.apache.tapestry5.corelib.mixins.GridCellContext'.  The duplicate object has been ignored.
