From what I observed:
Most one-off purchases are for the exact version you bought, therefore you should never update. Also if it became a Trial, just downgrade back using your installer to fix it.
The issue is that when you are using the Free version and download updates, the updated version automatically becomes a Trial. Moreover, the real issue is that the updated version will not indicate anywhere that it is a Trial/Master version. And this lies between either false advertisement or being a bug since 2016 and, as a software engineer myself, this is no excuse.
I just started using this Free version for a week and already got those annoying issues. I need more investigation, but currently this is clearly a solid product worth buying.