If this is a changed behavior after updating it looks to me like this is an unintended result of this feature:
l In the REST action configuration in WEBCON Designer Studio it is now possible to
build a request using JSON - Grid table structure containing objects, collections
and collections of values.
The image in the change log looks like the body could be based on the dictionary<string,object> like it is written in the form field. Maybe the json body was a string before and has been changed to a dictionary. But if the body is assigned to a field now the ToString returns the type of the underlying object instead of the simple string it was before.
So someone of you should open a support request, if it hasn't been done yet.
I would have to create an example, so I'm out of this.
Best regards,
Daniel