I can finally reproduce this. When I have a web action with a handle()
method like 

    def handle(self):
        cl = self.db.getclass(self.classname)
        cl.set(self.nodeid, status = self.db.status.lookup("feedback"))
        cl.set(self.nodeid, title = "Just a test")
        self.db.commit()

and we have an auditor (or reactor) that prevents the title change with
a Reject exception, then the first change (setting the status) will be
committed. Note that the commit() in handle() is never reached because
the second set() call will raise Reject. Note that the two changes above
will not usually be for the same class (they could be combined into a
single set call which is what the web-interface does when changing
several values).
Next step is to try to come up with a regression test for this.