Thanks for the speedy response and info so far ...
We had already installed the 831167 fix but the issue still occurs with http or https.
Puzzled .... we can reproduce it at will using the rather odd sequence of clicks and so forth described earlier ... note that it happens intermittently when using the file upload 'normally' - ie click button to open file dialogue, click file, click open ... click upload.
We reverted the application from https to http in order to determine if it was limited to SSL comms only as this is what the application should be using, however, checking packet data encrypted with modern cypher strengths is only for well seasoned!
So we are in rather a predicament ... it is definately occurring with http ... any suggestions on possible avenues - we are trying to avoid making application code changes at this stage ....
Many thanks again,