That's how I read 3(2), BM, as a statement of principle. He has no power to dish out money to himself or anyone else unless to the extent and in the circumstances mentioned. That's common sense and common law too, though sometimes it takes a statute like the Statute of Frauds or this one to recite it.
What does an intended beneficiary or other interested party do, to stop an abuse like the one prohibited ? Presumably he could apply, quia timet, to have the attorney removed and,in the meantime, stopped from distributing and, at a guess, the attorney would be personally liable for any act and consequent loss beforehand since his possession of them is in the nature of trusteeship. How would you go about tracing and retrieving the funds dispersed though? The offending party might be a man of straw and so pursuing him be of no benefit.