While poking around in the glibc source code I've found another one ;) There was a last minute ABI change for the syscalls: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=601cc11d054ae4b5e9b5babec3d8e4667a2cb9b5 The syscall windup in sysdeps/unix/sysv/linux/{preadv,pwritev}.c doesn't reflect that (yet). I think that code isn't compiled yet in rawhide due to kernel-headers not having the syscall numbers. That will change when kernel 2.6.31 hits the repo ...
Should be fixed in glibc-2.9.90-22.