I use PVD Version 0.9.9.14 on the Windows XP Professional SP2 OS.
Then I add a movie, with an actor.

Then I fill in the role of the actor in the movie.

Then I add another actor in the movie.

When I look at the first actor the role is gone

I import many actors and there roles of a movie via IMDB, but sometimes I want to add an actor to that movie, so all roles disappears and I must fill in all the roles by hand.