This question made me think of asking, but it's actually the third time I've come across it in the last few months. In one earlier case the user actually rolled back edits fixing their grammar.
This isn't regarding changes to the substance; the user wrote a post with grammar errors, another user fixed them, then the original user edited it again to add errors back.
In the previous cases I just left it alone, and I'm inclined to do so again. But then we have posts with bad grammar lying about that really should be fixed. It seems equally unproductive to engage in a discussion with the OP in the comments, along the lines of "please stop editing grammar errors into your post". Is this something a mod can address? Should the post be re-edited again with the hope the OP realizes their error and doesn't repeat the cycle?