Mighty plugin but it seems to mess up a bit in TinyMCE. Other buttons, that is extra/new ones from plugins, are removed. I tried to move your button to another row but it still think it is King :)
Forgot to add that in HTML view no buttons are kicked out.
Also on dashboard: Metaboxes cannot collapse/open with Shortcode UI as only plugin and using default theme.
My test install is local and default but have noticed same problem on other install with tons of add-ons.