I had this happen this night. It was in that state in the morning, so I did not see it happen.

It is on Win XPsp2. Java -version:

java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_04-b05)
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode, sharing)

Im heavily firewalled currently (outside my control), only outgoing TCP connections work via some NAT, no UDP transfers work.
Very few downloads complete in such an environment.

The computer is a leaf and had about 10 downloads pending, but none of them where downloading as I went to bed.