Hey there,
I'm running into a little trouble changing PresentValues of data points while the device which is sending the WritePropertyRequest is also subscribed to Confirmed COV notifications of that data point.

This is the error my device receives:

com.serotonin.bacnet4j.exception.ErrorAPDUException: ErrorAPDU(choice=127, errorClass=Device, errorCode=Operational problem)
	at com.serotonin.bacnet4j.transport.Transport.send(Transport.java:202)
	at com.serotonin.bacnet4j.LocalDevice.send(LocalDevice.java:370)

I'm not exactly sure what choice=127 means, but for some reason the target device doesn't process the WriteProperty request. Oddly enough, WriteProperty requests which are quickly sent after the first actually are successful.
Also, when using the UnconfirmedCOV service, WriteProperty requests do not produce any errors, and properties are written without issues.

Could this be a bug?