VS 11 Loses Chapter Titles

[mbs6]

I'm working on creating a DVD which has 66 chapters on it. When I go to "Create Disc" I am able to look at and edit the menus it will create. However, when I change the chapter titles from the defaults of Chapter001, Chapter002, etc., VS seems to randomly lose some of the titles I've typed in! When I close down the project and come back another time, some of the titles have gone back to the defaults. If I try correcting those, then others are missing next time! What am I doing to cause this?