Same problem here! Just when I find a great, time-saving plugin, it gets broken somehow. :(
I've been using Fast Image Insert successfully in Safari ... until today. Now the "Insert selected images", "Invert selection" and "Toggle items" buttons have disappeared. Without those buttons, the plugin loses its usefulness to me. What happened???
The problem occurs with Safari 4.0.3 on a Mac. Fast Image Insert is version 1.5.1.
Everything works fine in Firefox (3.5.3) as tomdebruin noted above, so that's what I'll use for now.