A link to a story about the Victorian driver false positive:
John De Jong paid out for drug-drive fiasco | News.com.au Top stories | News.com.au
False positives are the real problem. Searches for information about drug test false positives suggest that they may be caused by many different things, most of which you would have no idea about beforehand. As far as actual over the counter drugs go, it seems like almost all nasal decongestants (including inhalers) might cause false positives for amphetamines. As people have noted, codeine and poppy seeds can cause false positives for opiates. It is also likely that false positives can occur without any obvious cause at all.
I would be very interested to see the actual false positive rates for the test - presumably the manufacturer documents it. From what I can find, 5% may be conservative - so if they are aiming to conduct 6000 tests, 300 pilots may be unnecessarily stood down. I would certainly expect the false positive count to be much higher then the true positive count.