In their order manual they do state it might not be canceled or modified if you're less than 10 pips away from the marketOriginally Posted by ;
Note:
Clients that have an active order and want to modify or cancel the active order:
When the market rate is near the active order rate (1 to 10 points away),
the order modifiion or cancellation may not be approved. If this happens, your order will continue to be active.