Edit approval that changes the question - what should be done?

Question

Ref- Scan Barcode and QR code from the mobile screen itself

Edit history for this question shows that a moderator rejected the edit four months ago (for reasons I also agree with), but this edit is approved few minutes ago by OP so it stands approved (See How do suggested edits work?).

The approved edit brings about a fundamental change to the question, making the existing answers only partly correct and relevant. Someone visiting the question today (it is on the home page) may actually down vote the answers as they don't match the question body. It's another matter that the approved edit made changes to the body but not to the title of question.

I doubt if 7 years back when the question was posted, QR codes were a thing. Bringing that in the scope of question now, is meaningless.

To give another example, USB Type C charging wasn't around about four years ago. If OP of a question approves an edit that brings Type-C charging into the ambit, we would have a similar problem (if the question was posted pre Type-C days)

IMO, moderators should rollback the edit approval in this instant case. That's the easy part (hopefully moderators can do that based on this meta post, a cursory check threw up Rolling back a completely changed question)

How to ensure it doesn't happen in future is the difficult part since OP exercises similar power to that of moderator, in edit approval / rejection.

Answer 1

For the moment, I have edited the question to separate the new objective of OP (QR codes part) and mentioned it as a new paragraph along with the date on which the objective was introduced. I know that mentioning date was a redundant step as a reader can easily see the dates from edit history. However, given the problem at hand of invalidation and effectiveness/comprehensiveness (E/C) of the existing answers, I went ahead with redundancy.

Usually, whenever my answer was invalidated or its E/Cs reduced by an edit from OP I used to comment to OP that they should consider my work and efforts into consideration first since their edit is in gross disrespect of my efforts. That said, if OP reverted the edit than the problem was disposed of. But if OP persisted with the edit, I either marked my answer with the heading that it was answered with respect to original question (with hyperlink to corresponding edit) or I deleted my answer (in cases when the whole answer was invalidated).

These cases had happened mostly when I was not a moderator, and since I used to be the only answer contributor I used to choose deletion or edit of my own posts instead of moderator attention.

In your case though, I do not want to revert the edit because QR codes now are widespread in use and potential solutions to barcode question might have support for QR codes as well. Given the question quality issues, I wager we might (if we haven't already) end up with a duplicate of that same question (with "QR code" as the changed terms) and answers common to both.

For containing duplicate or common answers in this case alone I chose not to revert the edit.

That said, I share your concern. Had one or more answers been fully invalidated, I in all likelihood could have taken your suggested route.

How to ensure it doesn't happen in future is the difficult part since OP exercises similar power to that of moderator, in edit approval / rejection.

We can't unless we on technical level prevent OP from approving a rejected edit. But this change would have to be discussed on the network meta.

Personally, I'm not in support of preventing OP from approving a rejected edit. Often times, an OP approves a rejected edit when OP alone is able to make sense that the edit is aligned with their question's intent. The edit you mentioned is once in a while misuse of edit privileges by an OP. Unless statistics dictate that this problem affects a lot of our answer contributors or site's quality control, I suggest we put this proposal for rest until it gathers traction on network meta.