replica.lag.time.max.ms or doco bugged?

Howdy!

I've got a three node 0.8 cluster with replication factor three and
replica.lag.time.max.ms set to 2000.

Typical list-topic output looks like

topic: user.publish partition: 0 leader: 1 replicas: 2,1,3 isr: 1,2,3

I noticed though that when I kill (kill -9 PID) one of the brokers the list
of the ISR does not change. The doco states for replica.lag.time.max.ms "If
a follower hasn't sent any fetch requests for this window of time, the
leader will remove the follower from ISR and treat it as dead." According
to this I would expect that after 2000ms the killed broker would be removed
from the ISR list. Which doesn't happen. Not even after minutes.

Is this

a/ a kafka bug?
b/ a doco bug?
c/ a bug in my understanding of how it works?

Thanks in advance,
Sven