I resolve the problem in other chageset.

Sorry, I see the kind of modification you made.

The problem in this form was not corrected by your changset, but it still remained. In the lower left corner there was still a segment coming out of the building (two overlapping lines). The two extrusions are not the problem that needed to be corrected.

It took a while but I finally found the problem. The only thing I don't understand is how come JOSM didn't show me that kind of error that should be reported.

Sorry for the misunderstanding.

The shape of this building is now wrong.
The map is made to have correct data and not to be pretty to look at. If your software does not render this building correctly the correction should be done software side and not data side.
Thank you