Hi Mark,
Though I was not able to get the working of 'My Dispute Cases' but user has accepted the solution of using 'Find Dispute Cases'. I am not sure if it a standard bug in SAP but have encountered this many times that 'My Dispute Cases' reflects closed cases at times. Let me know if you have any inputs on this. I am marking this post as assumed answer though.
Thank you again
Regards
Pankaj Pareek