See images, moves the ImageUpload button next to the PrefixDiscussion.
Well, this is kind of bad luck, sorry to hear that. The Image upload has a float:left and I guess it is because the author wanted it to be left of the editor toolbar. Plugins are called alphabetically and so what happens is this:
ImageUpload is shown first with a float left so that it is placed directly beside of my plugin. With the standard theme the icon, the title and the dropdown of PrefixDiscussion are all in one row, by the way.
I would advice you to deactivate PrefixDiscussion and then rename every file and directory from "PrefixDiscussion" to "DiscussionPrefix" and inside the plugin search and replace also PrefixDiscussion to DiscussionPrefix. This way it is displayed before the Image Upload icon and everything should be fine.
Please give feedback if that worked for you, thanks!