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In the Merge dialog you can see the list of fields which are conflicting, their initial values, your values and the values submitted by other user. Use the the Changes Only button to show/hide non-conflicting bug fields as well. In the bug details form below the conflict list you cab change the values for the conflicting fields specifying values which you want to upload. By default the conflicting fields reflect your local changes. Click the Upload button to upload them to Bugzilla.