Actually the "leak" occured on the Jedi set. Prowse once said in a Starlog interview that it was pretty unpleasant for him working on the film after that. He also denied being the source of the leak.

There was also an interview with one of the producers around the same time, (Howard Kazanjian?) who joked about someone unnamed that leaked phony script info given to them.

Since Prowse donned the Vader costume for that VCR board game Kenner once made in the 90's, I presume Lucas gave his blessing?