Comment 4 for bug 420353

OK, then I suggest this feature is not useful in it's present form:

There is no evidence attached to show the bug really does affect upstream, e.g. the version that it occurs in. It is unlikely that someone had gone to the effort of downloading, building and testing an upstream version and yet not done the final step of filing the bug report. (Filing a report upstream only requires having an existing bug login, being familiar with the upstream bug tracker and copying some content from the LP bug. These steps are arguably easier than the download/build/test steps).

My experience with bugs marked as affecting upstream without bug numbers is there is no evidence that they really have been tested with an upstream version. At a glance the bug report looks like it has been sent upstream when it hasn't.

If the requirement is to have someone else send the bug upstream then there could be a "bug-upstream" group to subscribe bugs to. This is not a great solution as the person who tested the bug is the best person to respond to questions from upstream.

In reality most bugs should be marked upstream - any bug that is triaged and does not have an upstream bug link needs one opened. (Doing an advanced search for "Show bugs that need to be forwarded to an upstream bug tracker" for confimed/triaged bugs shows this currently). If any additional user input was required it would be a "this bug only affects Ubuntu" button.