I installed an update to the forum software over the weekend along with a few other tweaks, looks like it's one of them that's causing the issues.
It still posts your comments, just doesn't take you back to the thread.
If you guys can bare with me, I'll wait until tomorrow afternoon when it's silly o'clock UK time and run a wee check/backup/repair on it, see if that solves it.
Cheers, and apologies,
Aegis