ALT Linux su(1) keeps running user's $PATH (maybe other variables) when invoked 
without -l. This behavior is different from e.g. Debian and is confusing. 
Moreover, this behavior (neither default nor with -l) is not documented in any 
way:

       By default the user's shell is invoked directly, however, giving the 
argument flag -, su is  instructed  to  invoke
       the  shell  as  a login shell. This means that the current working 
directory will be changed to the home of the new
       user and the shell's first argument will be prefixed with a -.
[...]
       -, -l, --login
              Invoke the shell as a login shell.


Compare with Debian su(1):

       The optional argument - may be used to provide an environment similar to 
what the user
       would expect had the user logged in directly.
[...]
       The current environment is passed to the new shell. The value of $PATH 
is reset to /bin:/usr/bin for normal users,
       or /sbin:/bin:/usr/sbin:/usr/bin for the superuser. This may be changed 
with the ENV_PATH and ENV_SUPATH
       definitions in /etc/login.defs.
[...]
       -, -l, --login
           Provide an environment similar to what the user would expect had the 
user logged in directly.