[procps] sysctl reports missing variable that isn't (net.ipv4.tcp_allowed_congestion_control)

sysctl can list this variable, but apparently not set it. strace output is pretty useless:

open("/proc/version", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6d54f9000
read(3, "Linux version 3.2.0-24-generic ("..., 1024) = 143
close(3) = 0
munmap(0x7fe6d54f9000, 4096) = 0
open("/sys/devices/system/cpu/online", O_RDONLY|O_CLOEXEC) = 3
read(3, "0-3\n", 8192) = 4
close(3) = 0
open("/proc/sys/net/ipv4/tcp_allowed_congestion_control", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6d54f9000
write(3, "illinois westwood lp\n", 21) = -1 ENOENT (No such file or directory)
close(3) = 0
munmap(0x7fe6d54f9000, 4096) = 0
write(2, "error: \"No such file or director"..., 89error: "No such file or directory" setting key "net.ipv4.tcp_allowed_congestion_control"
) = 89
exit_group(-1) = ?

Here's listing and failing to set:

host ~ [0]# sysctl net.ipv4.tcp_allowed_congestion_control
net.ipv4.tcp_allowed_congestion_control = illinois cubic reno
host ~ [0]# sysctl net.ipv4.tcp_allowed_congestion_control="illinois westwood lp"
error: "No such file or directory" setting key "net.ipv4.tcp_allowed_congestion_control"
host ~ [255]#

Is this possibly related to a bad AppArmor profile? I've never encountered this on a non-Ubuntu system. On top of this, I can set net.ipv4.tcp_congestion_control with no error, and sysctl shows the change afterward.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: procps 1:3.2.8-11ubuntu6
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic x86_64
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Sun May 13 13:25:31 2012
InstallationMedia: Ubuntu-Server 12.04 LTS "Precise Pangolin" - Release amd64 (20120424.1)
ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
 LANG=en_US.utf8
 SHELL=/bin/bash
SourcePackage: procps
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.sysctl.conf: 2012-05-13T13:22:37.626745