I am experiencing the same behavior. I send post data to an /add.do endpoint. The originating post works fine. Following the redirect, soapui tries another post to an endpoint (view.do) that is expecting a get.
I am able to turn off redirects (properties of the step > lower left hand corner) for this and I no longer get the ugly 500 in my response window.
***** Log snippet *****
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "POST /mywebapp/customers/add.do?customerTag=tag9&description=description9&name=customer9&parent=1 HTTP/1.1[\r][\n]"Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "User-Agent: SOAPUI mywebapp Client/virtualX.2[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Content-Type: multipart/form-data; boundary="----=_Part_0_23483815.1299076411554"[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "MIME-Version: 1.0[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Host: qa01[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Cookie: $Version=0; JSESSIONID=74C8802F0E88D766DCCFD8EF0757A930; $Path=/mywebapp[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Expect: 100-continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Content-Length: 43[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 100 Continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 100 Continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "------=_Part_0_23483815.1299076411554--"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 302 Moved Temporarily[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 302 Moved Temporarily[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Date: Wed, 02 Mar 2011 14:33:30 GMT[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Location:
https://qa01/mywebapp/customers/view.do?id=70[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Content-Language: en-US[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Content-Length: 0[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Connection: close[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "Content-Type: text/plain; charset=UTF-8[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "POST /mywebapp/customers/view.do?id=70 HTTP/1.1[\r][\n]"Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "User-Agent: SOAPUI mywebapp Client/virtualX.2[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Content-Type: multipart/form-data; boundary="----=_Part_0_23483815.1299076411554"[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "MIME-Version: 1.0[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Expect: 100-continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Content-Length: 43[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Host: qa01[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "Cookie: $Version=0; JSESSIONID=74C8802F0E88D766DCCFD8EF0757A930; $Path=/mywebapp[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 100 Continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 100 Continue[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "------=_Part_0_23483815.1299076411554--"
Wed Mar 02 09:33:31 EST 2011:DEBUG:>> "[\r][\n]"
Wed Mar 02 09:33:31 EST 2011:DEBUG:<< "HTTP/1.1 500 Internal Server Error[\r][\n]"