On a separate note, I'd also like to suggest that it would be much smoother, easier, and reliable if JForex API offered a simple way to cancel an open order in any active state without closing out any open position (partial or otherwise) - ie. order.cancel(). Having to figure out when to use close() and/or setRequestedAmount is tricky, and depending on how they're used could lead to potential overlooked threading issues in the JForex API. I also merge orders after they appear to have been fully filled, so I wonder if the problem could be associated with that as well.

Regarding canceling order, IOrder.setRequestedAmount(0) is just an alternative to IOrder.close(). Hence, there is not much to figure out - simply use IOrder.close(). Please refer to the diagram:
https://www.dukascopy.com/wiki/#Order_state/Conditional_order_states_diagram
Please elaborate.