OttoR (2019-05-05 12:59:49+00:00): Hallo Frans,
I think something went wrong. To start, it is more common to review a HOT task in the HOT Tasking Manager, rather than using the OSM functionality for reviewing.
This helps in determining what tile you are refering to. Possible you used the OSM functionality, because it triggers an e-mail rather than the HOT Messaging system. I can understand this.

Looking at the specific changeset; using both the Bing as well as DigitalPremium imagery, these are actual buildings. Not the courtyard.

Also if you do a review of my profile, you would have seen that I have over 5.000 changesets, mapped over 78.000 buildings in 11 countries. You would think that it is unlikely I would consistently map courtyards for buildings or have not squared the buildings becuase of lack experience. ;-)

So yes I do use JOSM and the building tool, and I validate myself quite often, squaring buildings when not done so. 

I think that you are not refereing to task 5976 (which you commented on), but to #5977 - Cyclone Kenneth, Comores: Nzwani Central Buildings 1, and looking to this task, indeed here you did validate a lot of the tiles I marked as complete. However, if I did not square a building here, this is intentional, because the building is actually not square. Also where you assume I mapped the courtyard as a building, in my view this is a still a building..

To give a few examples:
Look for the tile with the football field. Just to the North - given the imagery, I believe this is a building with a basketball and tennis pitch on top. You changed the whole building to be a basketball field, which is incorrect.
Either it is a building, or it is a high fence, but not the whole area is a pitch. If it is not a building 'sports_centre' would be the correct tag to use.
When you look at the building with the supermarket to the East of this pitch, this is clearly a building with one or more floors; unfortunately due to the position of the sun, the shadow is very small, but you can see it is similar to what I beleive is the building underneath the pitches.*

If you move to the West of the pitch, I marked an open space as a square. you can see a few cars parked there. From there, when you follow the secondary road to the next main crossing, there is a building with a blue roof. I strongly beleive this building is not square.

On the opposite of the street of that blue roofed building, I think you removed a building because you think it is a courtyard. I beleive this is a building. Have a look at the white car in the streat, you can see that there is a darker area, which I believe are the several floors; it is just that the other buildings around it are higher. I marked two new buildings for your reference. Have a look and let me know what you think.

This village is very densly build with rooftops overlapping, at least the centre area. The same reason why it is hard to determine where the road network is running. The not so high resolution of the imagery is nog helping here.*

*Based on your comment I looked at some different imagery from another provider, which is a bit more high quality and even provides some street level photos. which makes me beleive it is a rather high fence of a stadium of some sort.