A member at rebelscum posted a video of them playing with a vintage Boba Fett prototype. When Boba Fett was going to be released in 1979 he was supposed to have a rocket that fired out of his backpack. However, just before the release a child was killed by choking on a similar missle from a Battlestar Galactica toy. When the Boba fett figure was released the missle was glued in and the spring mechanism removed. Some better pictures of what the prototypes look like can be seen at http://theswca.com/images-unpro/rocketfett-lslot.html
Boba Fett was first a mailaway figure so when kids did finally receive the figure a letter was also included to explain the change. An example can be seen at http://theswca.com/images-speci/mailaways/fett.html