kdPostWindowEventQNX will return KD_EOPNOTSUPP if the event type is not one of KD_EVENT_WINDOW_CLOSE, 
KD_EVENT_WINDOW_REDRAW, KD_EVENT_WINDOW_FOCUS, KD_EVENT_WINDOWPROPERTY_CHANGE, KD_EVENT_STATE, KD_EVENT_INPUT, 
KD_EVENT_INPUT_JOG, KD_EVENT_INPUT_POINTER, KD_EVENT_INPUT_STICK, KD_EVENT_USER, KD_QNX_EVENT_KEYBOARD, 
KD_QNX_EVENT_WINDOW_CREATE, KD_QNX_EVENT_WINDOW_REALIZE, KD_QNX_EVENT_WINDOW_PROPERTY, or KD_QNX_EVENT_WINDOW_CLOSE.

To answer your specific questions, the error code returned by kdGetError is not changed unless kdSetError is called or 
another OpenKODE function sets the value as specified for that function.

kdPostThreadEvent would normally be used to post events from one thread to another. However, this function isn't 
implemented in QNX yet, so your best be is to stick with kdPostWindowEventQNX for now.