You cannot have transferrable property rights if contracts aren't enforceable against third parties.
I think you're begging the question. Maybe
you can't have transferable property rights without enforcing contracts against third parties, because you have a particular belief about the nature of ownership (i.e. that it only exists to the extent that observers are contractually forced to acknowledge it), but that doesn't restrict the rest of us who aren't burdened with that belief.
Okay, fair enough. But whatever that other mechanism is that permits transferrable property rights, unless it's carefully rigged not to, it will apply to other types of rights as well. In any event, Libertarians really are split on this issue. There is no one "Libertarian view" on this.
Oh please, there's hardly a "libertarian view" on the definition of the color blue.
I don't think that's fair. While you can probably find a self-described Libertarian or two who holds any imaginable view, there are a large number of positions that the vast majority of Libertarians hold consistently and are consequences of Libertarianism's principles.
But if you take the position that no two Libertarians agree on anything, then there's really no answer to the OP's question.
I wouldn't be surprised to hear one of us say 'The market will sort it out'. And you know what? That's the answer to your little Hypothetical. The Market will sort it out.
I agree, most Libertarians would believe that the market would sort it out. However, their position on what role the legal system would play in that sorting will vary. But it's true, many 'defects' in the legal system can be worked around by contract. (For example, EULAs are one way Microsoft 'works around' perceived weaknesses in the law of copyright.)