limits.conf not working

I’m trying to set user limits by editing limits.conf

debian@beaglebone:~$ cat /etc/security/limits.conf

@audio - memlock 256000
@audio - rtprio 99
@audio - nice -19

The debian user is in the audio group yet when I ask for the current limits I get:

debian@beaglebone:~$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 3803
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 3803
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

after reboot, neither the max locked memory nor the real-time priority are being changed…
Any ideas where I could start?

I’m using the Debian Image 2015-06-29 Jessie snapshot.