From my perspective it seems that some progressives pride themselves on open mindedness yet are the most intolerant people I've seen when it comes to what they don't agree with. In that sense it seems like 'open mindedness' means 'close mindedness'.
Often times so-called "open-minded" people shun others who think exclusively. This is contradictory. If a person says that he/she is open-minded to different schools of thought, he/she should be open to the exclusive ones too.
When it becomes mind numbing.
When you're open minded about everything except things you reject.