Description of problem:
ps reads cmdline from /proc/*/cmdline
This file contains list of arguments separated with \0. ps rewrites all \0 with space, so it can use it and print it out as one string. 
This behaviour breaks ksh shell - in some special cases, ksh does not exec new script, but executes it within itself and just rewrites argv and zeroes out the rest. Because ps replaces even trailing zeroes with spaces, ps gives odd results. 
For example instead of
"./a foo" 
it prints 
"./a foo              "

The problem lies in readproc.c:read_unvectored(...)
    if(n){
        int i=n;
        while(i--)
            if(dst[i]=='\n' || dst[i]=='\0') dst[i]=sep;
        if(dst[n-1]==' ') dst[n-1]='\0';
    }
    dst[n] = '\0';

before the rewrite while loop, it should skip trailing zeroes:
while(i && dst[i-1]=='\0') --i;


Version-Release number of selected component (if applicable):
1:procps-ng-3.3.8-10.fc19

How reproducible:
always

Steps to Reproduce:
################### cut here #########################
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
  int i;
  char *p;
  for(i=1;i<argc;++i)
  {
    p=argv[i];
    while(*p) *p++='\0';
  }
  printf("%d\n",getpid());
  sleep(99);
  return 0;
}
################### cut here #########################
1) gcc -o reproducer reproducer.c
2) ,/reproducer foo bar baz
<PID>
3) echo "'$(ps -p <PID> ho args)'"

Actual results:
'./reproducer            '

Expected results:
'./reproducer'

Additional info: