I have also experienced the same exact thing. My up-vote @ 100% is .02 cents, but I push the button down and the rewards for the post I just up-voterd drops. I will go back and remove my vote and then again up-vote and the same thing occurs.
I also find that sometimes my vote will be worth 2cents then 1 cent and then back to 2 cents. Have been experiencing this since the harkfork. No clue to why any of this is happening.
Good luck.