alarm handler bug on OWS 7.22?

I've written an event handler and set the onconfig parameter correctly as I can see from online.log-file. I also can see from online.log, that - with some errors (or events) - my event handler is called by: /bin/shell -c event-handler ... This works fine. But when it is called this way: /bin/shell /bin/shell -c event-handler ... it does not work. Both calls can be seen in online.log but only the first makes my event handler work. Why? Is this difference in calling a bug in informix? Thanks in advance, Pascal