When a message about certain number of gained/losed XP point is shown, I'm already curious which actions were a reason to this, but very rarely know an answer.

From design point of view, I think this could be just a bit more detailed message of XP change, such as "you gained NNN XP points (2=login,3=upvoted)"

From implementation point of view, I can say nothing, and can easily understand that such improvement could not be made.

BTW can I browse my own XP history? (I think there is a way)

Best wishes to you all,
Chicken