I have a Mac, and I always add my smilies after I type a post. I never have any problem adding them anywhere in the post. Either on Cubits or here?
If I want to add a smilie into a post that I already posted, I click the smilie into the "new post" area at the bottom of the thread, to get the type equivalent, then I copy (on a mac that is Command C) it, then I click edit on the the post I want to edit, then insert my mouse pointer and click where I want the smilie and paste (Command V). Works like a charm.
(if you already posted, and you go to edit, the smilies are not available - that is why I came up with the above method)
I use Safari, but have you tried using Firefox? I know that is one of the things Dave always recommends.