caffeinate with launchd Doesn't Work when I Close My Laptop's Lid

I have a launchd task that periodically initiates a time machine network backup. I've had problems with corrupted sparse bundle disk images, which I've assumed is due to the either the computer sleeping during a backup, the NAS sleeping while the sparse bundle is mounted, or some combination of the 2. So, in order to fix this I run caffeinate with launchd task and have caffeinate run my script. I found, however, that the computer still goes to sleep when I close the lid, even when AC power is connected. I did a simple test, and found that caffeinate works as expected when I use it in a terminal, and does keep my computer awake, however, in that same test initiated with launchd/caffeinate the computer still goes to sleep while the script is running.

I'm running caffeinate with the -ims flags. In my simple test I used the following script:

#!/bin/sh

while true; do
    date | logger
    sleep 1
done

I monitor the system log with:

tail -f /var/log/system.log

I'm using OS X 10.9.5.

Update: To answer Buscar's question. When I run pmset -g I see the following:

Active Profiles:
Battery Power           -1
AC Power                -1*
Currently in use:
 standbydelay         4200
 standby              1
 womp                 0
 halfdim              1
 hibernatefile        /var/vm/sleepimage
 darkwakes            0
 networkoversleep     0
 disksleep            10
 sleep                180 (sleep prevented by UserEventAgent)
 hibernatemode        3
 ttyskeepawake        1
 displaysleep         10
 acwake               0
 lidwake              1