Server :: Script Running Ssh Commands (via Loop) Exiting After First Iteration?

One of my servers needs to issue an "apt-get update" command on each of the clients in a lab. However, after the first update, it exits. In trying to replicate the problem with a simpler script, I created the following which fetches the listings of multiple directories from a client:

NUM=0
cat paths | while read DIR; do
ssh server-name ls $DIR > /tmp/$NUM.txt
NUM=`expr $NUM + 1`
done

Again, after the first iteration, the script exists. I tried the following line too, but it made no difference:

bash -c ssh server-name ls $DIR > /tmp/$NUM.txt

The only thing that worked so far is this

xterm -e ssh server-name ls $DIR > /tmp/$NUM.txt