When tty is disconnected, press C-A will not work

Reproduce Steps

socat pty,rawer,link=/tmp/ttyS0 pty,rawer,link=/tmp/ttyS1 &
minicom -D/tmp/ttyS0 /dev/null

pkill -9 socat

Now text

Welcome to minicom 2.9

OPTIONS: I18n
Compiled on Jan  1 1980, 00:00:00.
Port /tmp/ttyS1, 22:35:12

Press CTRL-A Z for help on special keys                             +---------------------------+
                                                                    |                           |
                                                                    |  Cannot open /tmp/ttyS1!  |
                                                                    |                           |
                                                                    +---------------------------+

Actual Behavior

Now press C-A z will not pop up help. press C-A q cannot exit.

Expected Behavior

Press C-A X can work

Others

Press C-C C-A z and C-C C-A q can work. I doubt it should be related to interrupt.