Geocortex Essentials Workflow Update Graphics Layer activity Renderer.FromJson esriPMS negative xoffset does not work

I would like to display a call-out label at the left side of a point location on a Map, see the first screenshot. I am using Geocortex Essentials Workflow (GE version 4.14.2) Update Graphics Layer Activity to add a callout symbol on one graphic layer, and then add a text string on another graphic layer. 

The JSON for the text label: "{""type"":""simple"",""symbol"": { ""type"": ""esriTS"",""color"":[255,255,255,255],""xoffset"":-50,""yoffset"":6,""text"":""Label""}}"

The JSON for the image symbol: "{""type"":""simple"",""symbol"": { ""type"": ""esriPMS"",""angle"": 0,""xoffset"":-50,""yoffset"":0,""contentType"": ""image/png"",""imageData"": ""........"",""height"": 24,""width"": 60}}"

But the negative xoffset value of esriPMS shows as positive offset on the map (see the second screenshot). 

Wondering if anyone has run into similar issue and has a solution for it. Any suggestion is appreciated.