There was a strange problem happened last week. If I did su, everything works
fine, if I did sudo su, terminal became confused (after any key pressed, a
carriage return was also processed). I spent an hour to go thru login
scripts,where can be a problem, when I realized strange setting in sudoers.

Sudoers was copied from Sun/Solaris machine, and the syslog setting was there:
# Defaults specification
Defaults        syslog=auth
Defaults        log_year, logfile=/var/adm/sudo.log

The problem is, that /var/adm directory doesn't exist on linux OS.
I changed /var/adm into existing /var/log, and then the problem was gone.