Wow, I didn't even realize this was happening. I wonder if there's something in the code that awards the author regardless of time or if this is working as intended and if you immediately upvote you don't get curation rewards. 

Almost every post I've made I just leave the "upvote" box checked, and it's always been 0 weight. Never paid much attention. I'll have to watch myself how these numbers interact wth eachother!

Also, thanks for writing some interesting content that also features steemstats ;)