When reviewing a late answer, I scrolled down to check the question, to get some context. This question had a lot of comments, and the
show x more comments link was available. This of course lead to the entire comment list of the question being shown. But it also allowed me to up-vote a comment in that list. Which lead to the
I'm Done button getting activated.
In case the question's entire comment list is already visible (i.e. the
show x more comments link is not available), then voting on comments is not allowed.
Isn't this a bug? If I'm reviewing a late answer, why should a vote on a comment in the question be counted as reviewed?