customUnit not recognized in JSON exe/script advanced

I've modified the sample Demo Batchfile - Returns static values in four channels.bat to return a JSON result, instead of the original XML, but respecting all the tags names.

The resulting modified file is this one:

@echo off
REM Sample Exe/Script Advanced sensor        
REM Returns four sensor channels with static values to standard OUT
REM Predefines limits for one channel
REM < and > must be escaped in command line scripts

echo { "prtg": {
echo    "result": [
echo      {
echo        "channel": "Demo Minimum Example",
echo        "value": 3
echo      },
echo      {
echo        "channel": "Demo Disk Free",
echo        "unit": "Percent",
echo        "mode": "Absolute",
echo        "showChart": 1,
echo        "showTable": 1,
echo        "warning": 0,
echo        "float": 1,
echo        "value": 38.4487,
echo        "LimitMaxError": 80,
echo        "LimitMaxWarning": 37,
echo        "LimitWarningMsg": "My custom note for warnings",
echo        "LimitErrorMsg": "My custom note for errors",
echo        "LimitMode": 1
echo      },
echo      {
echo        "channel": "Demo Network Speed",
echo        "unit": "SpeedNet",
echo        "volumeSize": "MegaBit",
echo        "mode": "Absolute",
echo        "showChart": 1,
echo        "showTable": 1,
echo        "warning": 0,
echo        "float": 0,
echo        "value": 124487000
echo      },
echo      {
echo        "channel": "Demo Custom",
echo        "unit": "Custom",
echo        "customUnit": "Pieces",
echo        "mode": "Absolute",
echo        "showChart": 1,
echo        "showTable": 1,
echo        "warning": 0,
echo        "float": 0,
echo        "value": 855
echo      }
echo    ],
echo    "text": "Demo values. OS: %OS%"
echo   }
echo }

When I create the sensor the custom units are ignored. Instead of seeing something like the original XML script:

855 Pieces
38,4487 %

I get

855 #
38,4487 #

Have I missed any detail?

json prtg script sensor