In the base, it is wrong, what rendering does, should not effect good tagging, leave it as it is, is wrong. 
As you did not mention that you have seen it, I assume that "you walked over it" Not noticed the situation, why there was a multipolygon, recognize my fault.
But still set back as a polygon.
This looks like a mechanical, so there is now a double mistake. I aspected with such a cleaning, that you noticed it, if you did it on purpose, that is not okay.

Did you notice the slope=yes tag?