That's very odd. I tried it using this test program:

#!/usr/bin/perl

print "my pid = $$\n";

get_lock();
   print "enter return again:";
   my $x = <STDIN>;

sub get_lock {
   local($0) = "(acquiring lock)";
   print "enter return:";
   my $x = <STDIN>;
}
[download]

In another terminal I get:

$ /bin/ps 27940
  PID TTY      STAT   TIME COMMAND
27940 pts/0    S+     0:00 (acquiring lock)
$ /bin/ps 27940
  PID TTY      STAT   TIME COMMAND
27940 pts/0    S+     0:00 ./d0
[download]

I'm using Ubuntu 7.10.

Update: Ok, it does seem that you will lose the initial 'perl' from the COMMAND field when $0 is restored, but the script name should still remain. Don't know why that happens, and I also can explain yet your 'ww' output.