Imagine this scenario, DearReader. You have submitted your manuscript and the Associate Editor who has managed the review sends you the critiques with a recommendation for "minor revisions".
w00t! In like Flynn, amirite?
Now suppose as you are tidying up responses to the criticisms of the reviewers you find one reasonably substantive criticism that would be best addressed with the addition of another figure or two. This might even be for data that you have already, but left out of the original submission for some reason or other. You include it, package the thing up and re-submit the revised version of the paper.
The AE responds by essentially return-email that the manuscript has been accepted. Clearly, it didn't go back out for review. This is fairly typical, btw, that an AE will make the editorial decision that all criticisms have been addressed adequately.
When it comes to new data, however? That now have not been reviewed by peers...?
Is this a breakdown in the system? Has the peer-review stamp of approval been compromised in this case? Or is this an accepted part and parcel of the peer review process which is no different from the AE accepting the paper after minor stylistic changes in presentation , the addition of a few more caveats or citations to the Discussion or toning down the ELEVENTY language in the Abstract?