On Stack Overflow, I've recently (on the 20th of Aug) gained 10 reputation for an upvote on one of my answers.
If I check the reputation tab in my profile, it states "+10 upvote"
However, if I hover my mouse over my name in the top of the window, the tooltip shows +20 for that answer.
On the 7th of August I had +10 for that answer too, so it looks like you're aggregating all the scores for that answer for the current month.
Is this by design, or should scores not be aggregated in the tooltip?