There's a bug in the RI's FilterOutputStream that causes exceptions to be ignored. I'm unsure why they don't have a fix; perhaps they don't grasp how dangerous this problem is.
I've attached a program that demonstrates the bug. In order to cause a FileOutputStream.write() to fail, this lame program only runs on OS X where it's easy to create and unmount disks programatically. When executed, the program completes normally despite the fact that the second write fails.
Submitting a fix to Harmony will decrease compatibility with the RI, but in this case I feel it's justified. Concerns?
PS - I'm still waiting on the Apache volunteers to setup my commit access...