'File -> Preferences -> Modeling -> Body Type: Body or Sheet', changes unexpectedly..
'File -> Preferences -> Modeling -> Body Type: Body or Sheet' is a Session Setting.
This means that if it is altered by a user, journal, macro, NXOpen program, and not by a file, then it will remain set until altered again.New files or starting NX, by default will always be set to "Body Type: Solid".