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 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