ampersand in JSON body of a POST request break the service

Hello,
I have a POST with a JSON payload served by VW. If some string of the JSON
sent as request's body  contains the & character, the JSON gets divided at
the & sign and breaks the system.

For what I know & are not allowed on query parameters (so you need to
urlencode the string), but know nothing about the body. It's my fault or
perhaps there is a small problem in VW SiouX?

thanks

giorgio