redundant `next_ptr == 0` check in queue?

[copyrat90]

I really don't see why this check is required:

lockfree/include/boost/lockfree/queue.hpp

Lines 458 to 464 in ba92d67

	if ( next_ptr == 0 )
	/* this check is not part of the original algorithm as published by michael and scott
	*
	* however we reuse the tagged_ptr part for the freelist and clear the next part during node
	* allocation. we can observe a null-pointer here.
	* */
	continue;

The comment says it clears the next part during allocation, however looking at queue::node's constructor, it seems that it doesn't clear the tag;
Rather, it increases the tag to avoid ABA problem.

lockfree/include/boost/lockfree/queue.hpp

Lines 112 to 119 in ba92d67

	node( T const& v, handle_type null_handle ) :
	data( v )
	{
	/* increment tag to avoid ABA problem */
	tagged_node_handle old_next = next.load( memory_order_relaxed );
	tagged_node_handle new_next( null_handle, old_next.get_next_tag() );
	next.store( new_next, memory_order_release );
	}

By the time next_ptr == 0 check is performed, it is already guaranteed that head == head2, so the next_ptr must have set to the correct next pointer to the head's next node.
And it is guaranteed that pool.get_handle( head ) != pool.get_handle( tail ), so the next_ptr can't be nullptr.

Even if the head has been reused by the time when the check performs, the next_ptr should hold the previous next node value instead of nullptr.

Am I missing something here?