So despite having "Always use proximity" enabled in my call settings, it was still hit-n-miss on it actually working for me. Sometimes my screen would work after a call, sometimes it wouldn't.
I found
this post which mentioned changing a setting in
build.prop and rebooting... this seems to have fixed the issue for me. Their post mentions "
mot.proximity.delay" but my phone was actually "
ro.lge.proximity.delay". I also didn't bother doing the adb pull/push as described, I just used the adb shell to check the setting with grep, used sed to change it, then a reboot...
[root@ubuntu ~/droid/]: ./adb remount system
remount succeeded
[root@ubuntu ~/droid/]: ./adb shell
# cp /system/build.prop /system/build.prop.bak
<-- always make a backup 
# grep proximity.delay /system/build.prop
<-- checking current proximity delay setting
ro.lge.proximity.delay=100
# sed -i 's/proximity.delay=100/proximity.delay=25/' /system/build.prop
<-- changing it from 100 to 25
# grep proximity.delay /system/build.prop
<-- verifying change
ro.lge.proximity.delay=25
# reboot
After phone reboots... call your voicemail, and test the setting by placing hand in front of screen, removing hand, repeat. Then go drink beer