Icing separating from gingerbread

by Cheryl
(Agawam, Ma)

My pieces of gingerbread that are not supportive have been falling off my train, do you know why this wouyld happen? I used a gingerbread recipe with no eggs and added black food coloring to both the gingerbread and the icing. In the corners of the supportive pieces you can see how the icing has moved away from the gingerbread. I also have some lights that may have created a little heat however there is nothing on the outside and the decorative pieces have become unattached. The icing remains on the main structure but separates from the little pieces.