The lexical cue assumes that a pair of words differing in the first or last segment (like [kanaX] and [kanaK]) is more likely to be the result of a phonological process triggered by adjacent sounds, than a true semantic minimal pair.
this strategy clearly gives rise to false alarms in the (albeit relatively rare) case of true minimal pairs like [kanaX] ("duck") and [kanal] ("canal"), where ([X], [l]) will be mistakenly labeled as allophonic.