Chair of my committee keep adding and changing ideas I am trying to defend my proposal and I have a very inefficient professor as the chair of my committee. He keep adding and changing ideas consistently. I get the feeling that he doesn't really know the details of my work. During discussions with him, he picks up some elements and asks me to add ideas and tasks that aren't applicable. 

I am afraid that if I confront him (e.g. why his idea won't work, or what I don't like about it), he will take it personally. I spoke with one of his students and was told that he had picked a topic for her, which later on, an expert in that field deemed invalid.

He seems to be more interested in new topics that sound fancy or complex. The good part is that he is not very interested in the work itself or the result. What I mean that if I just want to please him I can through some of his ideas somewhere without much effort and he will be happy. After all, the ideas he picks are not within his area of expertise and he doesn't know much about them. But I can't do this for my proposal because it is hard to explain them to the rest of the committee members.
Any advice,
My advice is that the dissertation, and therefore the proposal, are the student's work.  It is the student's responsibility to pick a topic and execute it.  Faculty are not usually trained in project management so the student may need to act to keep the faculty member on track.  For example, you can tell the faculty member that their ideas are very interesting, but you need to complete your current project first.

More specific to your situation, a fourth year student should know more than their advisor about the student's work.