See Why is the oil future price negative? and Why do people buy negative interest rate bonds? The first question is the second most upvoted on this SE, the second is easily in the top 100. The most upvoted answer to each question turned out to be a lightly edited version of texts copied from other places. You can easily find them googling some of the more peculiar phrases, also the poster said as much after they were confronted with the issue.
There are several questions that arise:
Is copy pasting answers (with or without light edits) a legal problem? It is my understanding that SE answers fall under a Creative Commons license.
Does this SE have a non-legal problem with copy pasting answers (with or without light edits)? One could argue that the information is still useful, it still had to be found etc. The only reference to plagiarism I found on our meta was here.
If this is problematic, is there any possibility for automatic screening? (Such as Urkund.) I originally upvoted both answers without researching if they were original.