In order to say that a bug affects another source you currently have to click on "also affects distribution/package", and choose the current distribution and package. If you want to add only add a package, there should be a page where you don't have to choose the distribution.
In order to say that a bug affects another source you currently have to click on "also affects distribution/ package" , and choose the current distribution and package. If you want to add only add a package, there should be a page where you don't have to choose the distribution.