[Jython] Rule not executed, but no detailed error message

Some jython-rules that contain errors are not executed (openhab tells this in the error message, but actually they are executed, but “excepted” or aborted), but there is no log entry why.
There is also no entry in syslog about an exception. (BTW: I still can’t believe that there is no way to see exception directly in the openhab logging mechanism, see Exceptions in JSR223 rules (jython) are no longer shown in log (openhab2-daily)) .

Executing the rule below results in error message:

12:15:54.192 [INFO ] [RULES.LEDMODE ] - Rule executed LED-Mode Ian
12:15:54.214 [INFO ] [RULES.LEDMODE ] - Sunset
12:15:54.234 [ERROR] [e.automation.core.internal.RuleEngine] - Failed to execute rule ‘4f516a3a-2d7e-4d95-bea5-682c1b0576e7’: Fail to execute action: 1

So I can see that the rule is started and than aborted (exception?). There are no more messages related to this rule afterwards and no exception in syslog. (Other exceptions from jython rules are shown in syslog.)

Note: My question is, why there is no error message, not why the rule fails (I already found the issue).

class LedModeIan(SimpleRule):
    mode_table = {'On': (100,100,100,80),
                  'Off': (0,0,0,0)}

    def __init__(self):
        self.triggers = [
        self.mode_table.update({'Dimmed': (50, 50, 24, 0),
                                 'Sunset': (60, 100, 50, 0)})

    def execute(self, module, input):
        rlog.info("Rule executed LED-Mode Ian")
        if (unicode(items.ian_ledmode) == "Manual"):
            rlog.info("LED-Mode set to manual")
        (w, r, g, b) = self.mode_table.get(str(items.ian_t_ledmode), (0,0,0,0))
        rlog.debug("State of ledmode %s: %d, %d, %d, %d" % (unicode(items.ian_t_ledmode), w, r, g, b))
        rlog.debug("Table: " + unicode(self.mode_table))
        events.postUpdate("ian_t_led_W", str(w))
        events.postUpdate("ian_t_led_R", str(r))
        events.postUpdate("ian_t_led_G", str(g))
        events.postUpdate("ian_t_led_B", str(b))       


I have the same problem. Is there a solution?