I inspected what happened in one case, where I saw that a vote was cast at 50% and shortly after changed to 100%. When I checked the code, this scenario zeros out the vote weight, and means that curation rewards for the voter are zeroed out. 

I thought that it would make it as if you voted later but it turns out that it actually just zeros it. Wondering if this is something that will be changed in the future, since at least to me it is not what I would expect.

I'm not sure if all your cases are like that or not. By the way, if you do not recall these revote actions, I would recommend checking if autovoters are interfering with things.