Using third party SMS app on LG G3

[AC Question]

I installed a third party SMS app that I like quite a lot. Works great, nicer looking than the built-in version. A minor issue: overtime I turn on my phone, whenever I attempt to use the app, the phone tells me that in order to use all the features, it must be selected as the default messaging app. I then have to click the OK button, which seems to take care of it. It's a minor inconvenience, but it usually happens when I am trying to answer a time sensitive message, or trying to send one.

I have installed the app as the default messaging app. I've checked in settings any number of times. The phone doesn't seem to recognize this. Is there something I am overlooking, or is this just a built-in feature to discourage third party apps?

The phone is LG G3 Vigor. Running Android 4.4.2