- Create a new smiley.
- Enable CSS sprite mode for good measure. I'd imagine it happens without it too, though
- Make the smiley replace the following text: ':\' (without quotation marks)
- When posting a thread, select the smiley manually through the smiley chooser. The bug doesn't happen when typing :\ out.
- The smiley will not appear in the editor, but will appear in your post.