Broken su in current - trying to fix myself, help needed!

[Artem Kuchin]

>> if you try to run a very simple perl script:
>>
>> #!/usr/bin/perl
>> $com="/usr/bin/su root -c 'echo heck'";
>> system($com);
>> print "done!\n";
> 
> This works fine for me. If I run it as root (and change the user it's
> su'ing to to a normal user), it runs find and prints:
> 
> heck
> done
> 

OH MY GOD!!! I have posted this problem before and saw many 'me too'
reponses and thought that this problem is everywhere. After your and
Kostik's posts and decided to make a clean test. Turned off jails
and all custom kernel sysctls. Entered shell and run this cript - it printed:

heck
done!

I have rerun all configs and  started jails - still works. Then i remembered
that i have always run this script fro midnight commander.
Started mc
Pressed ENTER on this script and it got suspended.

Now i am lost, whose problem is this? su's or mc's? or both?
If i remove su from the script and run simply
system('echo heck');
from mc it work fine. With su it gets suspended.

--
Rrgards,
Artem