When I submit a POST request with "Web Services Tester", then the form parameters get corrupted as follows:

a) In the "Request Header" section I insert:
content-type=application/x-www-form-urlencoded

b) In the "Request Body" section I insert e.g.:
param_1=value_1
param_2=value_2

c) At the server side I receive just 1 form parameter, namely "param_1" having the value "value_1param_2=value_2".

I also tried to separate the enumeration in the "Request Body" section by a comma ",". Then the comma is just part of the concatenated string value.