bytesToString has an encoding parameter. If the bytes where not created using the default encoding the the IS JVM is running with, then you should pass in the encoding used to create the bytes.
If it is XML and the IS XML parser is converting the stream/bytes to String, it will follow the XML rules of looking in the XML prolog for the encoding attribute or default to UTF-8.
#webMethods#Integration-Server-and-ESB#webMethods-General