Perhaps you have encountered the Left-Rothbardian idea before. If you haven't, then Brad Spangler's "Market Anarchism as Stigmergic Socialism" is a good introduction. The article contains a quote from Rothbard that sums up the essence of the argument:
"The only genuine refutation of the Marxian case for revolution, then, is that capitalists' property is just rather than unjust, and that therefore its seizure by workers or by anyone else would in itself be unjust and criminal. But this means that we must enter into the question of the justice of property claims, and it means further that we cannot get away with the easy luxury of trying to refute revolutionary claims by arbitrarily placing the mantle of "justice" upon any and all existing property titles. Such an act will scarcely convince people who believe that they or others are being grievously oppressed and permanently aggressed against. But this also means that we must be prepared to discover cases in the world where violent expropriation of existing property titles will be morally justified, because these titles are themselves unjust and criminal."
Now, I ask, what if we don't know whether a particular property title is just or unjust? Rothbard himself offers an answer;
"If we know that these conditions hold, then there is no problem, for the identification of both aggressor and victim is remarkably clear-cut. But if we don’t know whether these conditions obtain, then (applying our rule), lacking a clear identifiability of the criminal, we conclude that the land title and the charge of rent are just and legitimate and not feudal." The Ethics of Liberty, chapter 10
Now, what is wrong with this position? Quite simply, it allows the ruling class to take advantage of confusion and ignorance about historical facts.
Consider Rothbard's hypothetical example which he uses to refute the "utilitarian" position of siding with all currently-existing titles by default. His scenario is that a King is faced by a rising libertarian movement, so the King proclaims the "state" to be dissolved but claims the kingdom's territory as his private property, renames taxation rent, etc. Now, the "utilitarian" libertarians would not be able to criticize the king. But all this king has to do to swindle the Rothbardians is to destroy historical records of his violent conquest of the land. Sure, they can probably guess that the land was stolen, but they wouldn't know for sure, so they'd need to side with the king by default.
In short, Rothbard replaces the utilitarian cry of "You can't revolt against private property, peasant scum!" with "You can't revolt against private property until you've done loads of historical research, peasant scum!" A similar premise can be found lurking in his "Confiscation and the Homestead Principle" - the workers can take over the factory, but only after they've researched how much money it gets from the government, and only if it's above Rothbard's arbitrary threshhold.
I can understand why Rothbard would come up with rules like these. He has accepted the principle of violently-enforced property - in order to prevent roaring, violent conflicts, there must be a rule for every case, and in cases of uncertainty, there must be a default owner. To side with the current owner is merely an extension of "innocent until proven guilty," right? The absolutists need to classify all property titles in the binary categories "legitimate" or "criminal." Clearly it would be bad if we classed all property as "criminal" until proven otherwise, yes?
But there's a third category - "indeterminate" - which cannot be ignored in this imperfect world. The violent propertarian must throw the "indeterminate" cases in with the "legitimate" cases - otherwise, his principle would create massive violent conflicts. A Macchiavellian conservative, interested in winning the violent propertarians over to the defense of the status quo, can easily do so by expanding the "indeterminate" category, by spreading confusion and uncertainty. That is their real "cunning stratagem."
That is precisely what the "right-libertarians" have done in the recent debate between left- and right-libertarians triggered by Roderick Long's articles at Cato. The right-libertarians are running the smoke machine. That's why they've shifted the debate onto the field of limited liability, where the mighty Legal Jargon SmokeMaster 5000 is ready for use. And since many left-libertarians are still mired in the absolutist, binary distinction between "legitimate" and "criminal" property, they stand around swinging their swords at the smoke.