Esta página pode ajudá-lo. Um trecho:
Bash allows users to do very advanced things when defining shell prompt, including colours and propagation of information into xterm title. Unfortunately, when you want to use mc (Midnight Commander) in conjunction with bash prompts, you may find, that not all advanced escape sequences are handled by mc properly. To overcome this issue you can have a special prompt just for mc.
O que você queria:
if ps $PPID |grep mc; then
PS1="mc: \w"
fi