I believe that often non-native people use the language more correctly than natives. Being a native speaker doesn't mean you will get a correct text. There have been quite a few times I had to correct the corrections of native Hungarians in the Hungarian section in order not to mislead the learners. As an English teacher, I sometimes correct entries written in English, although I'm not a native speaker. But I have a C level in English, I use it every day, so this should be enough.

I do not see why it bothers you.  If you do not like it or do not trust it (for any reason), just ignore it.

Not to mention that sometimes it can give you an insight about the language itself and how it is used (but ok that is a logical leap, so I will not insist on that).

I fail to see why one would be bothered by it.  You do not like it.  Ignore it and move on to the native speaker corrected text, if you think it is better for you.  As simple as that.

Camilo, this also applies to people who are not teachers, but have a C level in the language in question. I think that in writing non-natives can help just as much, while in speaking, native speakers know best which phrases sound natural in a situation and which don't. But there are differences here as well, some words are completely natural in one part of a country, while in the other one, people haven't even heard about these. 

I'm torn on this one. As Tünde mentioned earlier, people with advanced levels in the target language are more mindful or grammar. And like parvin, I can usually spot errors that other people make in my target language, even though I'm not a native speaker.

That said, I will say that at one point in my French learning, I was being helped by someone who was non-native, but was fluent and had been living in France for a very long time. Her grammar was impeccable, and she was very helpful in correcting my writing. But at the same time, I would also receive private messages from native French speakers who would tell me that even though her grammar was correct, the tone of the language that she was using and the style of writing was very old-fashioned or quite "soutenu", and no one really talked like that in everyday French.

So, for learning wise, I think it's fine. But if your goal is to assimilate in the culture, probably not so much.

I agree with you but I myself sometimes correct some easy English entries specially thoes which are just 2 or 3 lines. But I try my hardest to correct them well without any mistakes.

I read almost 80% of English entries but I just try to improve my English more and correct mine by noticing others mistakes but never correct them.