In reply to Offwidth:
Basically when you login, UKC set a couple of cookies going 'this person is logged in'. If you've had a tab open, pre-login, or the cookies have been cleared, then UKC sez 'no cookie, not logged in, can't reply'. Even tho it may say you're logged in at the top of your screen. Very simply.
I'm not a PHP programmer (python guy mainly) but I suspect that fixing it from a UKC perspective isn't that easy, hence it being a bit ropey.
Post edited at 12:43