Thick red circles around buildings' corners - ???

A couple of days ago I've drawn a few buildings (e.g. way osm.org/browse/way/119774654) close to another in a block, in a changeset 8591706, which ...

potlatch locked up and unable to save edited data

OK, my first complaint :-) in osm.org/user/kerosin/diary/14153 and immediately followed by Ticket #3836 (see http://trac.openstreetmap.org/ticket/3...