Thank you for your enquiry.
According to Novell, a defect prevented the OnReply event from firing when choosing an item from the Reply dropdown button (as opposed to clicking the Reply button, then choosing an option). This was fixed in GroupWise 6.5 SP1.
Perhaps there is a GroupWise field test fix available for 6.0.x?
Alternatively, you could experiment with changing when OnReply is fired, ie. before or after GW event.
I hope this helps.