[Chimera-users] ribbon causes coordinates changing

Dear chimera users, I've a problem with ribbon. I've a DNA molecule where the two last base pair is an uncommon T-T pair. When I select these bases to display the ribbon, the coordinateds of the last atoms are changed. Seem that the new position are the end of the ribbon. The chimera version I'm using is 1.5rc1 on a windows7 PC. I attacch the session that represent my problem. The session is saved such to visualize the problem: look at the end of the blue and red ribbons to detect it.