It has happen two times. I put two buildings that are the same (two electric plants for example), and they don't join!! Thats terrible because three of the same does not produce as much as three joined, I check. I bought things in the game so I cannot delete the base. Also, you should be able to use your special boxes (I dont know the name of them in english, the ones that have cards), in other bases if you have not open them. Please help with my problem!!! To delete it and build it again doesn't work, I tried!!

I found the problem. It's not a bug, it was so simple. When I upgrade both buildings so each were upgraded at the same grade, they joined!!! I comment it in case someone else has the same issue.