Given how randomly it happens, I believe there is a real bug in Terminator; but if you want to force the broken state, just open 'mc' and run 'pkill mc' from another terminal, your scrolling will be broken.
A way to debug this kind of thing is to run e.g 'mc > trace.txt'. Then type 'exit', hit return, and mc will quit. You will get all the escape sequences from mc in trace.txt to inspect.
Getting this with 1.91 on Arch, it likes to happen during package updates for some reason.
I found a hacky workaround - add this to your $PS1:
\[\e[?1049l\ e[?2004l\ e[?1006l\ e[?1002l\ e[?1001r\ e[?1l\]
It'll fix it as soon as you get to a prompt.
Given how randomly it happens, I believe there is a real bug in Terminator; but if you want to force the broken state, just open 'mc' and run 'pkill mc' from another terminal, your scrolling will be broken.
A way to debug this kind of thing is to run e.g 'mc > trace.txt'. Then type 'exit', hit return, and mc will quit. You will get all the escape sequences from mc in trace.txt to inspect.