gerrit removes review scores when pushing a topic

I pushed a set of changesets to a topic (http://codereview.qt-project.org/#/t/9/) and all of them were reviewed and given a score, then after a while I noticed that one of the changes was wrong, so I amended it and re-pushed the topic. Now gerrit took away all scores that changesets got even for changesets that were not modified whatsoever - even for changesets whose SHA-1 haven't changed.