Hm indeed, multitail reports tons of:

| mc: *** info
| mc: Warning: closing connection
| /usr/sbin/gpm[2220]: *** warning [daemon/processconn.c(133)]: 
| /usr/sbin/gpm[2220]: Failed gpm connect attempt by uid 1000 for vc /dev/tty0

in syslog if it gets start inside GNU screen on tty4, so this needs some
attention what's going wrong here.