We have come across a case where the rules engine does not fire the top priority (top salience) rule. After a lot of careful debugging, it seems that the BinaryHeapQueueAgendaGroup implementation (and most likely the supporting BinaryHeapQueue) has a bug. It is not a common case and it was hard to reproduce. We have put together a junit test to show the problem. The test "replays" the trace from the case where we show the error (sparing you from all the complexity of the actual rules and produced it). I will attach the JUnit test and the trace file that drives the test.