This is now https://trac.sagemath.org/ticket/21743
I have further problems (now with 7.5beta0 + #21743), sending new line during installation of an experimental package (cryptominisat) is ignored here:
https://github.com/sagemath/sagecell/blob/master/contrib/vm/container_manager.py#L461
The terminal got stuck on the [Y/n] question and then continued when I pressed Enter myself. Any clue or solution for this one?
That's a stale ticket that would allow one to turn of the prompt, but the real problem is "communicating with Sage" - I am trying to provide an answer to the question by sending a newline through the pipe, but it is ignored.