uniq() returns a duplicate record

I'm using ember 2.6 and the uniq() return a duplicate records even if I used the uniq()

Even if I used the uniq it does still return the duplicate records, my question is my approach below is to return the uniq but it still return a duplicate record

foos: computed.alias('model.foos'),
bars: computed.mapBy('foos', 'bar.content'),
uniqBars: computed.uniq('bars'),