Pictures duplicated on iMac, iPhone and iPad

I have a problem of duplicate pictures on all my devices: Photos on iMac, iPhone 6 and iPad Air 2.

The issue on the iPad is older but the problem is now occurring on iMac and iPhone and is happening since the release of Photos for iMac.

I have manually removed the duplicates on the Mac, reset the iPhone and deactivated the Photo Stream everywhere but it did not help.

Is anybody having the same issue?

Thanks