https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=db2e718a47984b9d71ed890eb2ea36ecf150de18 I stumbled on the bug and reason for this patch in December. I've been waiting for this to be fixed in the kernel to add a regression test for it. Now that the fix is in, I should remember to do that.
Added a stand alone tests/uns_test.c for this bug as part of this CL: https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=572b1f8099c05e2840ae66d52d8bee8e547bad39 I'll make a 2.60 release before including its execution in quicktest.sh
s/2.60/2.50/
Fixed with: https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=2c99ecd7ee8580cced618dd9d16473f15e778e5e