Using exists together with facts of the same type can break auto-retraction of logically asserted objects

I assert 3 Lesson objects in my memory.
I got 1 rule, which creates logically asserted HardConstraint objects.
In some cases (not always), those logically asserted objects aren't retracted when they should be, which leads to HardContaints just adding more and more. They aren't logically retracted as they should be when:

• exists is combined with fact selections of the same class
• the modified object trigged the rule by the exists part, not by the the fact selection part

I 'll attach a maven 2 configured proof of concept to repreduce it:
mvn install eclipse:eclipse idea:idea
Run net.sf.tabudrool.app.TabudroolApp
Click "Load unsolvedSchedule2.xml" (the second button on the left)
Notice the HardConstraint = 2 at the bottom
Click "Move lesson"
Move "[net.sf.tabudrool.domain.Lesson-1] 0: teacher0 + group0" to timeslot 1.
Notice that HardConstraint = 3 instead 1 at the bottom,
because - as you can see in the log - the previous HardConstraint objects didn't get retracted.

Here's the drl:

rule teacherCanOnlyTeachOneGroupAtATime
when
$lesson : Lesson($id : id, $teacher : teacher, $timeslot : timeslot)
exists Lesson(id > $id, teacher == $teacher, timeslot == $timeslot)
then
System.out.println(" teacherCanOnlyTeachOneGroupAtATime: " + $lesson);
assertLogical(new HardConstraint(1));
end

Here's a log:

teacherCanOnlyTeachOneGroupAtATime: [net.sf.tabudrool.domain.Lesson-1] 0: teacher0 + group0
teacherCanOnlyTeachOneGroupAtATime: [net.sf.tabudrool.domain.Lesson-0] 0: teacher0 + group0
[ObjectAsserted: handle=[fid:9:9]; object=net.sf.tabudrool.domain.HardConstraint@1f42731]
[ObjectAsserted: handle=[fid:10:10]; object=net.sf.tabudrool.domain.HardConstraint@53abbb]
2006-08-03 19:24:35,796 [AWT-EventQueue-0] INFO net.sf.tabudrool.swingui.WorkflowFrame$MoveAction.actionPerformed(WorkflowFrame.java:201)
Moving [[net.sf.tabudrool.domain.Lesson-1] 0: teacher0 + group0] to [1]
[ObjectModified: handle=[fid:7:11]; old_object=[net.sf.tabudrool.domain.Lesson-1] 1: teacher0 + group0; new_object=[net.sf.tabudrool.domain.Lesson-1] 1: teacher0 + group0]
teacherCanOnlyTeachOneGroupAtATime: [net.sf.tabudrool.domain.Lesson-1] 1: teacher0 + group0
[ObjectAsserted: handle=[fid:11:12]; object=net.sf.tabudrool.domain.HardConstraint@1c8b884]

As you can see: net.sf.tabudrool.domain.HardConstraint@1f42731 and net.sf.tabudrool.domain.HardConstraint@53abbb weren't retracted (at least one should be).

Earlier this week I posted a dud jira issue, as far as I can tell from discussing on irc (with conan), this looks like a genuine issue...