Are you running with V7 or V8? And are you running with the latest release of whichever one you have?
Somewhere in the depths of my memory I seem to recall a problem similar to this which was fixed by a maintenance release. But I could be thinking of something else slightly similar.
Sorry, I don't have time to seek out the reference just now. But in any case do check that you have all the updates you are entitled to.
This was indeed a bug which was corrected in the maintenance release Monarch 7.02 (and of course all subsequent versions of Monarch). I am guessing you are running Monarch V7. Simply download the Monarch 7.02 update from [url="http://www.datawatch.com/support/downloads/I702_upd.exe"]here[/url] and you should be all set.
Please also see [url="http://www.datawatch.com/support/whats-new-version-seven.asp"]this page[/url] for details on this update (see 2nd bullet under Bug Fixes).