3rd party SMS apps won't stay default - Default settings resets automatically



I'm having a very annoying issue regarding 3rd party apps for SMS's in 4.4.2: they just won't stay default no matter what.

If I set any 3rd party app as default, the settings are cleared every few minutes, making the stock app default again. If I disable the stock app and make the 3rd party app default, Android will set Hangouts as default on its own moments later. If I uninstall Hangouts, leaving the 3rd party app as the ONLY enabled app capable of handling SMS, it'll still ask me when I open it!!!!

I'm all out of things to try here and I can't find anything similar online. It'd be greatly appreciated if anyone could help figure this out.

Thanks in advance