One place to start with teams whose mentor/student working relationship seems out of balance would be to have all the mentors (and students) re-read the mentor guide on the FIRST website.
The "its all about me" is inappropriate behavior for students or mentors. (A sudden and unannounced change of design/implementation behavior is a statement of "its all about me" - "I *know* better than you", etc. in my humble opinion. I've seen this attitude from both students and mentors. This type of power struggle often is just the tip of larger submerged group communication & trust issues.)
FIRST Mentoring Guide
"Allowing and encouraging independent thought"
"Mentors grow and learn new perspectives from the young minds brainstorming and working under their tutelage."
"Team members learn technical and organizational skills well enough to be assigned some mentoring roles."
"Provide students with opportunities to make choices, both good and bad."
"Let the kids know that they will have a large part in building the team’s robot once they have learned and practiced the necessary skills…...and follow through with your promises."