I'm pretty sure there is a limited vouch window. I can vouch the first but not the second, I would imagine you should be able to as well. As far as the poster goes, my best guess is the account is somehow flagged as a bit? I've seen a few accounts where every comment they make shows up as flagged-dead, but I've never been quite sure why.

Anecdotal, but I feel like I've seen an uptick in flagging attacks or aggressive reactions to benign comments. It's odd.