Hi,
I am sorry but I have also tested this and could not reproduce this problem with SoapUI 4.5.2.
In your screenshot, it seems you have a complex form, which comes from your WADL probably. That may be causing the problem. The WADL I used to test this is fairly simple.
Can you provide us with a similar WADL (you can remove sensitive information and just leave enough for the problem to still be present) so we can try it in our tests?
Also, if you want to attach a JSON file (or any file) to your POST (or PUT) request, you can just set Media Type to "multipart/form-data" and then add the files in the Attachments tab. The file will be sent in the body of the message (if you use encryption, it will be encrypted).
Regards,
Renato
SmartBear Software