Fact #1. According to QtDN rules, adding a tag gives user 2 points.
1) A thread has been started by user Alice. She puts a tag for it and as a result she gets 2 points.
2) Bob logs in QtDN and opens the thread started by Alice.
3) Bob removes a tag that has been added by Alice.
4) Bob adds the same tag as Alice added earlier.
5) Bob gets 2 points for adding a tag.
This looks wrong, i.e. 5th step should not take place. Such mistake can be used by users to increase the number of points and as a result get higher ratings for doing nothing.