Well yes its the quick reply that I'm referring to - perhaps I need to re-phrase my question.
When typing in this message in the quick reply editor the delete key does not work but the backspace key does.
Well what do you know, it's working right now.
This is very strange as this is a frequently recurring issue which I find annoying, the backspace always works but the delete key doesn't when using the quick reply editor (and only in the quick reply editor)! - but right now it is working and I haven't even restarted the PC in between my previous post and this!
Oh well - I guess I'll just have to see if it happens again and try to determine the lead up circumstances.