Create two facts with the same start time, each having two equal tags. FactTree widget will show them as 4 separate facts. This problem is caused by method itertools.groupby(). It requires facts already sorted by key (fact.id), but facts are sorted by fact.start_time and tag.name. I would suggest sorting facts by fact.start_time and then by fact.id. We can ignore sorting by tag names, it is not helpful and it is causing this very annoying issue. I tested it and it works well.
how do you create two facts with same start time?