Hey Miriam,
The problem is for both Google+ for Business and in Google's Places for Business dashboard. The duplicate listings aren't showing up in the SERPs, because Google is deactivating one of the "duplicates."
So, let's say I claimed an unverified Google+ for Business page for A Generic Business. I verify the page, fill out all the info, add photos, etc. and it's live and listed on Google and looks splendid. All the info is correct, confirmed, etc.
Then, say, a week later, I log into my account and there's a red banner across the top of my Google+ for Business dashboard saying that my listing has been marked as a duplicate. A duplicate of what? As always, I searched and only found one, unclaimed listing and that's what I moved into my account and verified.
I called Google and asked what happened, and they said they're doing a "cleanse," in which they're looking over both Google Places for Business listings and Google+ for Business pages and making "automated adjustments."
I've had multiple clients' business pages marked with this red banner, because Google generated and automatically verified a true duplicate of what it thought the page should look like, and then just pushed my listing out.
I hope this explanation helps make a bit more sense.