Usefulness of max_transid in the tree search?

Hi,

I just had a look at how btrfs ioctl searches the tree for new items and
while looking at the code I've noticed that maximum transaction id as specified in the search is rather useless.
If I understand right, transaction id is stored in a header of each node.
Thus when any item of the node gets modified, new transaction id gets recorded. So when you give the search some maximum transaction id, you will not receive items in nodes where some item has been modified in a later transaction. That seems like a rather useless set of items to me... Or am I missing something?

Honza