Modbus TCP two way data exchange

I want to use the UR as Modbus client exchange data in both directions.
A Modbus server is set up in the network.

I defined a Register Input with Address 0 Name MODBUS_1
And a Register Output with Address 1 Name MODBUS_2

All connections are fine!

If I change the value of MODBUS_2, I can see the value on the server (using a second client , reading some registers) !

If I change the 1st register (by the second client) , I expect to see the value in MODBUS_1.
But this dose not work.

What did I wrong ?