Its an oversight. I just moved it into the panel so it will be consistent in the next release. Had not noticed it as this is a seldom used admin page and it looks fine in most of the skins. I'm not really sure that it should be inside there though even though it is inside there on some pages, but it should be consistent. You can easily style it regardless of its container using the breadcrumbs class.
On the content system pages the breadcrumbs are not inside panelwrapper.