There is a karma threshold for downvoting comments. It's not clear to me why you should ever have been able to ... perhaps your memory is at fault in this regard.
No I remember the down voting symbol. They two together used to look like a parallelogram now it's only a triangle. Maybe there was a glitch in the system
This isn't terribly interesting but I believe you actually need to pass 500 for it to be active. I sat at 500 for a bit the other day with this account and couldn't downvote but hitting 501 changed that.
