:terminal : normal-mode editing for shell prompt

• nvim --version: NVIM v0.3.1
• Vim (version: ) behaves differently? no.
• Operating system/version: Arch linux
• Terminal name/version: Alacritty/0.1.0
• $TERM: xterm-256color

Steps to reproduce using nvim -u NORC

nvim -u NORC +terminal
In the terminal mode go into insert mode, write something.
Go back into normal mode(still in terminal) try to change or delete 
the search terms. 

Actual behaviour

cannot make changes, 'modifiable' is off

Expected behaviour

do whatever would normally happen to text whenever you use cw, D, dw etc.

I could probably solve this by just setting the buffer modifiable, but is there some problems with this since this is the default behavior? is there a preferred way of doing this? And how do i apply it only to the terminal buffer and nothing else all the time?

Thanks.