G'day Rob,

I investigated this a little. Firstly, I can confirm what you're seeing.

Opening replies to that node shows the radiobuttons (++/--/+=0) and a [vote!] submit button. These all seem to work as normal.

I looked at #59098. This is a single reply with no child nodes. I voted (++) on it: now showing "Reputation: 7".

I also looked at #153429. This reply starts a subthread; it has multiple branches; one branch goes to "Re^5". I voted (++) on this reply, as well as the Re^5 node: all worked as usual and "Reputation: ..." now replaces the radiobuttons.

I refreshed the parent node (csv2png.pl - Line Graphs from a CSV file) after each operation: "Reputation: ..." was shown as appropriate; a [vote!] button remained absent.

All Reputations were greater than one, so I'm not the first to vote on these; however, I have no idea of the "who", "when" or "how" of these other votes.

It would appear that, at this point at least, you can vote on any of the nodes (except the parent), albeit with some minimal hoop jumping.