Took me a while to figure this one out
Injected - Your screen dump holds the answer actually, you must be using the 'Reply' buttons the left hand side of the page.....
These actually reply to THE THREAD rather than to individual posts (there is a difference, trust me
I'm pretty sure if you use the Reply buttons in the posts on the RHS of the screen you will get the 'Go Advanced' option & be able to get the smilie drop-down...
(There is an option to choose the advanced editor straight away via the Edit Options link in your control panel / Quick links above)
Cheers - Frank