There is a bug report about the current networkmanager memory leak at launchpad since March now. At that time the current Release was not even out. But the maintainers at Ubuntu are so passionately careless about it that they haven't even commented on it since then.
There are several people watching the bug and of course thousands affected with NetworkManager being in the standard installation of at least Ubuntu and Kubuntu, but the maintainers keep their hands still. A fix is also out and has been successfully applied and a package was released, too. It just never went into the current distribution.
This shows how the community can care so much about important bugs, if the appropriate people don't respond, many Linux users are just as helpless as when they use Windows. But I really doubt that such a major memory leak would remain unfixed for such a long time even in any current Microsoft product.
If you want the bug fixed for you, you can do so manually, I posted links to the fixed packages a while ago.