TCP binding has stopped working for my setup

I have been controlling my opentherm thermostat from openhab for quite a while. I use the TCP binding to send a command to my opentherm gateway and I receive MQTT messages back giving me the status.

The strange thing is that in openhab version 1.6.2 this worked well but has stopped working in later versions of the tcp binding. I now keep the 1.6.2 version of the binding in the openhab add-on directory to keep my interface with the thermostat working.

My item definition is:

String ot_setpoint_send "Thermostaat override [%.1f °C]" (Thermostat) {tcp=">[pitherm.local:7686:'REGEX((.*))']"}

And in version 1.6.2 this works well and when I send a command I get these log lines:

2016-03-28 09:02:07.762 [INFO ] [enhab.model.script.Thermostaat] - Central Heating on
2016-03-28 09:02:07.764 [INFO ] [enhab.model.script.Thermostaat] - TT=20.5
2016-03-28 09:02:07.765 [DEBUG] [i.s.RegExTransformationService] - about to transform 'TT=20.5' by the function '(.*)'
2016-03-28 09:02:07.765 [DEBUG] [t.protocol.internal.TCPBinding] - transformed response is 'TT=20.5'
2016-03-28 09:02:07.949 [DEBUG] [t.AbstractSocketChannelBinding] - Picked WriteBufferElement [Channel=Channel [item=ot_setpoint_send, command=1, direction=OUT, remote=pitherm.local/, buffer=, isBlocking=false, isReconnecting=true, channel=/, host=pitherm.local, port=7686], buffer=TT=20.5
2016-03-28 09:02:07.949 [DEBUG] [t.AbstractSocketChannelBinding] - Sending TT=20.5
2016-03-28 09:02:08.201 [ERROR] [t.protocol.internal.TCPBinding] - transformation throws exception [transformation=null, response=TT: 20.50
2016-03-28 09:02:08.201 [DEBUG] [t.protocol.internal.TCPBinding] - transformed response is 'TT: 20.50
2016-03-28 09:02:08.201 [DEBUG] [i.s.RegExTransformationService] - about to transform 'TT: 20.50
2016-03-28 09:02:08.201 [DEBUG] [t.protocol.internal.TCPBinding] - transformed response is 'TT: 20.50'

When I upgrade to the latest 1.8.2 version it does not work and I get these log lines:

2016-03-29 07:48:00.801 [INFO ] [enhab.model.script.Thermostaat] - Central Heating on
2016-03-29 07:48:00.803 [INFO ] [enhab.model.script.Thermostaat] - TT=20.5
2016-03-29 07:48:00.803 [DEBUG] [i.s.RegExTransformationService] - about to transform 'TT=20.5' by the function '(.*)'
2016-03-29 07:48:00.803 [DEBUG] [t.protocol.internal.TCPBinding] - transformed response is 'TT=20.5'
2016-03-29 07:48:01.018 [DEBUG] [t.AbstractSocketChannelBinding] - Picked WriteBufferElement [Channel=Channel [item=ot_setpoint_send, command=0, direction=OUT, remote=pitherm.local/, buffer=, isBlocking=false, isReconnecting=false, channel=/, host=pitherm.local, port=7686], buffer=TT=20.5, isblocking=false] from the queue
2016-03-29 07:48:01.018 [DEBUG] [t.AbstractSocketChannelBinding] - Sending TT=20.5 for the outbound channel />pitherm.local/

Am I doing something wrong or is openhab tcp binding not working any more?