How to delete a read only working set in Eclipse

I can't delete some working set, when I cleared up my projects working sets. The properties of this working set is as following. How can I delete it?

My eclipse version: Juno SR1 20120920-0800

You cannot delete it.

The "Other Projects" working set is a special working set. It exists to show you projects that are not explicitly inside a working set.

Why are you trying to delete it?

The only time you should care about it is if you have multiple working sets in your workspace. The "Other Projects" working set is very useful if you have Top-Level Elements->Working Sets selected in your package explorer (it's under that little triangle menu):

In this example, I've defined two working sets, Android and Collage to organize code in my workspace. Any projects not assigned to either of these working sets will appear under Other Projects so I can still see them (and possibly drag them to other working sets).