This keeps being stated.
Wasn't there a clause that there needed to be 'best efforts' (or something similar) to resolve the situation? That could then be used to appeal to a court, presumably the ECJ. Fail on 'best efforts', and the backstop would be invalid.
Belief that it would tie things indefinitely is based on any individual's opinion that the EU would want to keep the UK tied and troublemaking - I don't think that would be the case, but I appreciate that some (and this isn't aimed at anyone particularly, although the Daily Express is obvious!) consider the EU to be a great Machiavellian evil who the ECJ would submit to at all times.