On polygraphs and paedophiles

I was interested to hear this snippet of news on the radio today. The government have apparently been conducting a trial in the Midlands involving subjecting convicted sex offenders out on licence to lie detector tests as a way of monitoring their ability to adhere to their licence conditions. The trial, independently assessed by the University of Kent, has been hailed a success because offenders subjected to the test admitted to twice the number of breaches than did controls given standard interviews only.
There are obviously a few ethical issues here, one being that when this scheme is rolled out nationwide and adopted as policy, what will happen to offenders who are deemed by the machine to be lying as polygraph tests are notoriously unreliable. Although claims by the manufactures say that they can be correct up to 95% of the time, independent studies suggest 65% (not a lot more than chance) is a more likely figure.
Part of this is due to the fact that the physiological traits measured by polygraphs (blood pressure, pulse, respiration, and skin conductivity) are only partially indicative of the assumed stress brought on by lying. They can be indicative of stress for other reasons (not least being falsely accused of lying) and they can be absent if the subject is a practiced liar, which sex offenders notoriously are.
Regardless, the results of the trial convincing as they are still require some explanation and I suspect that ignorance of the true efficacy of lie detection is at the root of it. Those subjects who were interviewed under the polygraph probably believed that they could be caught out in a lie and therefore were more forthcoming with the truth, whereas, the controls were almost certainly behaving as they normally would. Which is, from a law enforcement and risk control point of view, still a good argument for using the technique. I just wonder how long its efficacy will last if offenders ever realise that the risk of being caught out is minimal.
Assuming the government and the probation service are aware of the dangers of relying on polygraph evidence and reaonable checks and balances are in place to protect offenders who are genuinely reforming and adhering to their licence, I see no harm in this policy. But the rational that is being presented to the general public for its utility is I think spurious and probably intentionally so.