I'll agree that copy paste of sections of even a straight up midi only project sucks.. As the OP say's you get unpredictable results . It should be logical and easy to do.
Drag and copy, put the now time on the measure line you want, and paste ( x amount of times) move over and make room.. What always happens to me is a big mess with only some tracks moving and then stuff hidden underneath the paste, so you get a cacophony of sound. Sometimes it works ,, but often it doesn't.
I generally write it off as just me not knowing what I'm doing , but still it would seem a basic function that could certainly be a little more user friendly. I swear it was easier back in 6- 7 and 8.5