Yes I know that this might sound like a previous question but bear with me I think its a bit different.
- I come across an answer that I think is wrong.
- I downvote.
- I start writing a comment on why I downvoted. Of course at this point the brain has engaged and starts to question some possible assumptions that lead to the downvote which makes me less sure the downvote is deserved.
- I remove the downvote.
- I go away and do a bit of test/research to check my assumptions and find them correct.
- I return to the answer and attempt to re-apply my downvote.
- Fail: "Vote to old to be changed, ..."
I agree with the reasons for this limitations for upvotes but I don't agree that a removal of an existing downvote is tantantmount to an upvote.