When I need to create a master-detail relationship, I use the wizard to set that up. Needed one today, but the MD is not working! If I select a master then the detail keep on giving me the same result.
Please verify that the cache property of your detail dataset is set to false. Caching is used to prevent unnecessary traffic, but on a detail dataset, the full dataset needs to refresh when the master changes. Please verify, otherwise we will contact you for more details as it is working well in our environment.